Study package · AP Microeconomics

AP Microeconomics study package

Everything you need to prepare for the AP AP Microeconomics exam in one place: course overview, per-unit notes, practice sets, a full-length practice exam with answer key, and a printable summary sheet. Works alongside the timed AP Microeconomics practice exam and the score calculator.

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Course overview

AP Microeconomics – Complete Study Package

AP Microeconomics focuses on the principles of economics that apply to the functions of individual decision-makers, both consumers and producers, within the economic system. The course places primary emphasis on the nature and functions of product markets and includes the study of factor markets and the role of government in promoting greater efficiency and equity in the economy.

Exam Format

Section	Type	# of Questions	Time	Weight
I	Multiple Choice	60 questions	70 minutes	66.7%
II	Free Response	3 questions	60 minutes	33.3%

FRQ Structure

FRQ 1 (Long, 10 points): Usually involves perfect competition, monopoly, or a combination of models
FRQ 2 (Short, 5 points): Often focuses on consumer choice, production costs, or a specific market structure
FRQ 3 (Short, 5 points): Often focuses on factor markets, externalities, or public goods

Units and Exam Weight

Unit	Topic	Exam Weight
1	Basic Economic Concepts	12–18%
2	Supply and Demand	20–25%
3	Production, Costs, and Perfect Competition	22–28%
4	Imperfect Competition	15–22%
5	Factor Markets	8–12%
6	Market Failure and the Role of Government	8–12%

Key Graphs to Master

Supply and Demand (with shifts, surplus/shortage, price controls, taxes)
Consumer/Producer Surplus (with deadweight loss)
Cost Curves (MC, ATC, AVC, AFC)
Perfect Competition (firm and market)
Monopoly
Monopolistic Competition
Labor Market
Negative/Positive Externality
LRAC with Economies of Scale

Study Package Contents

00-overview.md – This file
01-unit1.md through 01-unit6.md – Detailed unit notes
02-practice-unit1.md through 02-practice-unit6.md – Practice problems
03-full-practice-exam.md – Full practice exam
03-full-practice-exam-answers.md – Answer key
04-summary-sheet.md – Quick reference summary
05-exam-strategy.md – Test-taking strategies
06-presentation-outline.md – Presentation outline
07-audio-script.md – Audio review script

Unit notes

Unit 1: Basic Economic Concepts

Key Topics

Scarcity, opportunity cost, and tradeoffs
Production possibilities curve
Comparative advantage and gains from trade
Economic systems
Marginal analysis

Scarcity and Opportunity Cost

Scarcity is the fundamental economic problem: resources are limited while wants are unlimited. Every choice involves a tradeoff. The opportunity cost of any choice is the value of the next best alternative foregone.

Marginal Analysis is central to microeconomics. Rational decision-makers take an action if the marginal benefit (MB) exceeds the marginal cost (MC). They continue until MB = MC (the optimal quantity).

The Production Possibilities Curve (PPC)

The PPC shows all possible combinations of two goods an economy can produce when all resources are fully and efficiently employed.

Key Features:

Concave (bowed out): Increasing opportunity costs — resources are not perfectly adaptable
Straight line: Constant opportunity costs — resources are equally productive in both uses
Points on the curve: Efficient
Points inside: Inefficient (unemployed/underutilized resources)
Points outside: Unattainable with current resources
Shifts of the PPC:
Outward: More resources, better technology, improved education, institutional changes
Inward: Resource destruction, natural disasters
Worked Example: An economy produces capital goods and consumer goods. Producing more capital goods today leads to more economic growth (a larger outward shift of the PPC in the future) because capital goods increase the economy's productive capacity.

Comparative Advantage and Trade

Absolute Advantage: Producing more output with the same resources, or the same output with fewer resources.

Comparative Advantage: Producing at a lower opportunity cost. This is the basis for mutually beneficial trade.

Worked Example:

	Wheat (tons/day)	Cloth (yards/day)
Country A	8	4
Country B	2	2

Country A: OC of 1 wheat = 4/8 = 0.5 cloth; OC of 1 cloth = 8/4 = 2 wheat
Country B: OC of 1 wheat = 2/2 = 1 cloth; OC of 1 cloth = 2/2 = 1 wheat
Country A has a comparative advantage in wheat (0.5 < 1). Country B has a comparative advantage in cloth (1 < 2).

Terms of trade must fall between the two opportunity costs. Here, 1 wheat should trade for between 0.5 and 1 cloth.

Total output with specialization:
Country A produces only wheat: 8 wheat
Country B produces only cloth: 2 cloth
Without specialization: If each divided time equally, A would produce 4 wheat + 2 cloth, B would produce 1 wheat + 1 cloth = 5 wheat, 3 cloth
With specialization: 8 wheat, 2 cloth. If they trade 3 wheat for 1 cloth: A has 5 wheat, 1 cloth. B has 3 wheat, 1 cloth. Both are better off than without trade.

Economic Systems

Command Economy: Government makes all decisions about production and distribution. (e.g., North Korea)
Free Market Economy: Individuals and firms make decisions based on price signals. (e.g., closest to pure market: Hong Kong)
Mixed Economy: Combines market forces with government intervention. (Most modern economies, including the US)

Property Rights and Incentives

Well-defined property rights are essential for efficient market outcomes. When people own resources, they have incentives to:

Maintain and improve those resources
Invest in them for future returns
Trade them to those who value them most

Common Mistakes

Confusing absolute and comparative advantage. A country can have an absolute advantage in both goods but should still specialize according to comparative advantage.
Calculating opportunity cost incorrectly. Always express the OC of one good in terms of the OTHER good (not in dollars).
Thinking the PPC shifts when we reallocate resources. Moving along the PPC does not shift it. Only changes in resources or technology shift the PPC.
Adding all opportunity costs. The OC is only the NEXT BEST alternative, not the sum of all alternatives.

Self-Check Questions

Country X can produce 20 cars or 10 computers. Country Y can produce 10 cars or 10 computers. Calculate opportunity costs and identify comparative advantages.
Draw a PPC that shows increasing opportunity costs. Explain why the curve is concave.
If a student has 10 hours to study for two exams, and her PPC is a straight line, what does this imply about her ability to switch between studying for each exam?
Explain why property rights are important for economic efficiency.
What is the rule for rational decision-making using marginal analysis?
If two countries have identical opportunity costs, will trade be beneficial? Explain.

Unit 2: Supply and Demand

Key Topics

Demand and supply determinants
Market equilibrium, surplus, and shortage
Consumer and producer surplus
Price elasticity of demand and supply
Income elasticity, cross-price elasticity
Tax incidence and deadweight loss
Price ceilings and price floors
Consumer choice theory

Demand

Law of Demand: As price increases, quantity demanded decreases, ceteris paribus. The demand curve slopes downward.

Shifts in Demand (non-price determinants):

Income: Normal goods (demand ↑ with income); Inferior goods (demand ↓ with income)
Prices of related goods: Substitutes (price of A ↑, demand for B ↑); Complements (price of A ↑, demand for B ↓)
Tastes and preferences
Number of buyers
Expectations of future prices or income
Movement along vs. shift: Only a change in the good's OWN price causes movement along. All other changes shift the curve.

Supply

Law of Supply: As price increases, quantity supplied increases. The supply curve slopes upward.

Shifts in Supply:

Input costs (↑ costs → supply shifts left)
Technology (improvement → supply shifts right)
Number of sellers
Expectations
Government policies (taxes, subsidies, regulations)
Prices of related goods in production (if the price of a substitute in production rises)

Market Equilibrium

Equilibrium: Qd = Qs. No surplus or shortage.

Surplus (above equilibrium): Qs > Qd → price falls
Shortage (below equilibrium): Qd > Qs → price rises

Consumer and Producer Surplus

Consumer Surplus (CS): The difference between what consumers are willing to pay and what they actually pay. Graphically, the area below the demand curve and above the price.

Producer Surplus (PS): The difference between the price producers receive and the minimum they would accept. Graphically, the area above the supply curve and below the price.

Total Surplus = CS + PS — This is maximized at market equilibrium (allocative efficiency).

Deadweight Loss (DWL): The loss of total surplus that occurs when a market operates at a quantity other than the equilibrium quantity. Shown as a triangle between the supply and demand curves.

Elasticity

Price Elasticity of Demand (PED)

Measures the responsiveness of Qd to a change in price.

PED = (%ΔQd) / (%ΔP) (use absolute value for categorization)

Type	Total Revenue and Price	Description
Elastic	Ed	> 1	Move opposite	Q changes more than P
Inelastic	Ed	< 1	Move same direction	Q changes less than P
Unit elastic	Ed	= 1	No change
Perfectly elastic	Ed	= ∞	—	Horizontal demand curve
Perfectly inelastic	Ed	= 0	Move same direction	Vertical demand curve

Determinants of demand elasticity:

Availability of close substitutes (more substitutes → more elastic)
Proportion of income spent on the good (larger share → more elastic)
Time (longer time horizon → more elastic)
Necessity vs. luxury (necessity → inelastic)
Definition of the market (narrow → more elastic)

Price Elasticity of Supply (PES)

PES = (%ΔQs) / (%ΔP)

Supply is more elastic in the long run because firms have more time to adjust production.

Income Elasticity of Demand (YED)

YED = (%ΔQd) / (%ΔIncome)

YED > 0: Normal good
YED < 0: Inferior good
YED > 1: Luxury normal good
0 < YED < 1: Necessity

Cross-Price Elasticity (XED)

XED = (%ΔQd of Good A) / (%ΔP of Good B)

XED > 0: Substitutes
XED < 0: Complements
XED = 0: Unrelated goods

Taxes and Subsidies

Per-unit tax on sellers: Shifts supply curve left (up) by the amount of the tax.

Creates a deadweight loss triangle
Buyers pay more (Pd > Pe)
Sellers receive less (Ps < Pe)
Tax burden = Pd - Ps (the tax wedge)
Tax incidence: The burden is shared based on elasticity. The MORE INELASTIC side bears MORE of the burden.

Subsidy to sellers: Shifts supply curve right (down). Buyers pay less, sellers receive more. Creates DWL from overproduction.

Price Controls

Binding price ceiling (set BELOW equilibrium): Creates a SHORTAGE. DWL results.

Binding price floor (set ABOVE equilibrium): Creates a SURPLUS. DWL results.

Consumer Choice Theory

Total Utility (TU): Total satisfaction from consuming a given quantity. Marginal Utility (MU): Additional satisfaction from consuming one more unit.

Law of Diminishing Marginal Utility: As consumption increases, the additional satisfaction from each additional unit decreases.

Utility Maximization Rule: A consumer maximizes utility when: MUa / Pa = MUb / Pb (for all goods consumed)

If MUa/Pa > MUb/Pb, the consumer gets more utility per dollar from good A and should consume more A (and less B), which decreases MUa (diminishing MU) until the ratio is equalized.

Common Mistakes

Confusing a shift with a movement along. Price changes = movement; everything else = shift.
Misidentifying substitute vs. complement cross-price elasticity sign. Substitutes = positive XED; Complements = negative XED.
Drawing DWL on the wrong side of equilibrium. DWL always represents the LOST surplus from producing too little or too much.
Thinking inelastic demand means demand doesn't change at all. It means Qd changes proportionally LESS than P changes.
Forgetting that consumer surplus is below demand and above price. Producer surplus is above supply and below price.

Self-Check Questions

If the price of peanut butter rises from $3 to $4 and the quantity demanded of jelly falls from 100 to 80 jars, calculate the cross-price elasticity. Are peanut butter and jelly complements or substitutes?
A tax of $2 per unit is placed on sellers of a good. If demand is perfectly inelastic, who bears the burden of the tax? Is there deadweight loss? Explain.
Draw a supply and demand graph showing a binding price floor. Show the surplus, the change in CS and PS, and the DWL.
If a consumer is maximizing utility and the price of good A doubles, explain how the consumer's consumption will adjust.
Explain the relationship between total revenue and price elasticity of demand.
A tax is placed on a good with elastic demand. Will the deadweight loss be relatively large or small? Explain using a graph.

Unit 3: Production, Costs, and Perfect Competition

Key Topics

Production functions and marginal product
Short-run and long-run costs
Cost curves (MC, ATC, AVC, AFC)
Profit maximization
Perfect competition: short-run and long-run equilibrium
Efficiency in perfect competition

Production in the Short Run

The short run is a period in which at least one input is fixed (usually capital). The firm can vary labor but not its plant size.

Total Product (TP): Total output produced.

Marginal Product (MP): The additional output from one more unit of labor. MP = ΔTP / ΔL

Average Product (AP): Output per worker. AP = TP / L

Law of Diminishing Marginal Returns: As more of a variable input (labor) is added to a fixed input (capital), the marginal product of the variable input will eventually decrease. This is why the MP curve eventually falls.

Relationship between MP and AP:

When MP > AP, AP is rising
When MP < AP, AP is falling
MP intersects AP at AP's maximum

Cost Curves

Short-Run Costs

Fixed Costs (FC): Costs that do not change with output (rent, insurance).

Variable Costs (VC): Costs that change with output (wages, materials).

Total Cost (TC) = FC + VC

Marginal Cost (MC) = ΔTC / ΔQ = ΔVC / ΔQ

MC is the cost of producing one more unit
MC eventually rises due to diminishing marginal returns
MC intersects ATC and AVC at their MINIMUM points
Average Total Cost (ATC) = TC / Q = AFC + AVC

Average Variable Cost (AVC) = VC / Q

Average Fixed Cost (AFC) = FC / Q
AFC always decreases as output increases (spreading fixed costs)
Relationships between MC, ATC, and AVC:
When MC < ATC, ATC is falling
When MC > ATC, ATC is rising
MC intersects ATC at ATC's minimum
Same relationship between MC and AVC

Long-Run Costs

In the long run, all inputs are variable. The firm can choose its plant size.

Long-Run Average Total Cost (LRATC): The lowest possible ATC for each output level, given that the firm can choose any plant size. It is an envelope of all the short-run ATC curves.

Economies of Scale: LRATC decreases as output increases. Reasons: specialization, bulk purchasing, use of efficient technology.

Constant Returns to Scale: LRATC stays the same as output increases.

Diseconomies of Scale: LRATC increases as output increases. Reasons: management complexity, communication problems, bureaucratic inefficiency.

Perfect Competition

Characteristics of Perfect Competition

Many buyers and sellers (price takers)
Identical (homogeneous) products
Free entry and exit
Perfect information
Because firms are price takers, the demand curve facing each individual firm is PERFECTLY ELASTIC (horizontal) at the market price.

Profit Maximization Rule

A firm maximizes profit by producing where MR = MC.

For a perfectly competitive firm: P = MR = AR = D (since the firm is a price taker, every unit sold adds exactly the price to total revenue).

So the rule becomes: P = MC

Important: The firm should produce where P = MC, but only if P ≥ AVC (shutdown condition). If P < AVC, the firm should shut down in the short run.

Short-Run Profit Outcomes

Economic profit: P > ATC at the profit-maximizing quantity
Normal profit (break even): P = ATC (zero economic profit, but normal accounting profit)
Economic loss but continue producing: AVC < P < ATC
Shut down: P < AVC (the firm would lose more by producing than by shutting down and paying only fixed costs)

Short-Run Supply Curve

The firm's short-run supply curve is its MC curve ABOVE the minimum AVC point. Below minimum AVC, the firm shuts down.

The market short-run supply curve is the horizontal sum of all individual firms' supply curves.

Long-Run Equilibrium

In the long run, firms can enter or exit the market.

If firms are earning economic profit → new firms enter → market supply shifts right → price falls → profits shrink
If firms are suffering losses → firms exit → market supply shifts left → price rises → losses shrink
Long-run equilibrium: P = MC = ATC (minimum ATC)

At long-run equilibrium:
Zero economic profit (normal profit only)
Productive efficiency: P = minimum ATC
Allocative efficiency: P = MC
The firm produces at the lowest possible cost

Efficiency in Perfect Competition

Productive Efficiency: Producing at the lowest possible cost (minimum ATC). Achieved in both short-run and long-run equilibrium.

Allocative Efficiency: Producing the quantity where P = MC (the value to consumers equals the cost of production). This maximizes total surplus. Achieved in long-run equilibrium.

Common Mistakes

Confusing MC intersections. MC intersects ATC and AVC at their MINIMUM points, not maximum.
Thinking firms always produce where P = MC. They only produce if P ≥ AVC. If P < AVC, shut down.
Confusing economic profit and accounting profit. Economic profit = total revenue - (explicit + implicit costs). Zero economic profit means the firm earns a normal profit.
Thinking the market demand curve is horizontal. The market demand slopes downward. Only the INDIVIDUAL FIRM'S demand is horizontal in perfect competition.
Confusing short-run and long-run. In the short run, firms can earn profits or losses. In the long run, entry and exit drive economic profit to zero.

Self-Check Questions

Draw the cost curves (MC, ATC, AVC) for a perfectly competitive firm. Identify the shutdown point and the break-even point.
A perfectly competitive firm has TC = 100 + 2Q + Q². If the market price is $12, what quantity should the firm produce? Calculate its profit or loss.
Explain why the MC curve must intersect the ATC curve at its minimum point.
In long-run perfectly competitive equilibrium, explain why both productive and allocative efficiency are achieved.
Distinguish between economies of scale and diminishing marginal returns.
If the market price falls below minimum AVC, what should the firm do? What is its loss equal to?

Unit 4: Imperfect Competition

Key Topics

Monopoly: characteristics, profit maximization, efficiency
Price discrimination
Monopolistic competition: characteristics, short-run and long-run
Oligopoly: characteristics, game theory
Comparing market structures

Monopoly

Characteristics

Single seller facing the entire market demand curve
No close substitutes for the product
High barriers to entry (patents, economies of scale, government licenses, control of key resources)
Price maker (the firm chooses the price by choosing the quantity)

Sources of Monopoly Power

Natural monopoly: A single firm can supply the entire market at a lower cost than two or more firms due to extreme economies of scale (e.g., utility companies)
Government-created monopolies: Patents, copyrights, licenses
Control of key resources
Network effects (e.g., social media platforms)

Revenue for a Monopolist

P > MR for all units after the first (because to sell an additional unit, the monopolist must lower the price on ALL units)
MR curve lies below the demand curve
When demand is linear (P = a - bQ), MR = a - 2bQ (same intercept, twice the slope)
Total Revenue (TR) = P × Q

Profit Maximization

The monopolist maximizes profit where MR = MC.

Find Q* where MR = MC
Go up to the demand curve to find P* (the price consumers pay)
Go down to the ATC curve to find the average cost
Profit = (P - ATC) × Q

Monopoly vs. Perfect Competition

A monopoly charges a higher price and produces a lower quantity than a perfectly competitive market would
A monopoly creates a deadweight loss because it produces less than the socially optimal quantity
P > MC in monopoly (not allocatively efficient)
P > minimum ATC in monopoly (not productively efficient)

Price Discrimination

Price discrimination is charging different prices to different consumers for the same good based on willingness to pay.

Conditions for price discrimination:

The firm has market power (price maker)
It can identify different groups with different willingness to pay
It can prevent resale (arbitrage)
Degrees of price discrimination:
1st degree (perfect): Charge each consumer their exact maximum willingness to pay. Captures ALL consumer surplus as profit. Zero DWL.
2nd degree: Charge different prices based on quantity purchased (quantity discounts, block pricing).
3rd degree: Charge different prices to different demographic groups (student discounts, senior discounts, geographic pricing).

Regulating Monopolies

Average cost pricing: Set P = ATC. The firm breaks even (zero economic profit). Reduces but does not eliminate DWL.
Marginal cost pricing: Set P = MC. Achieves allocative efficiency but the firm may incur losses if P < ATC.

Monopolistic Competition

Characteristics

Many firms (like perfect competition)
Differentiated products (branding, quality, location, service)
Free entry and exit (like perfect competition)
Some market power (firms are price makers but face competition)

Short-Run Profit Maximization

Each firm faces a downward-sloping demand curve (due to product differentiation)
Profit maximization: MR = MC
The firm can earn economic profit, normal profit, or incur losses in the short run

Long-Run Equilibrium

Due to free entry and exit, economic profit is driven to zero in the long run
The firm produces where MR = MC and P = ATC (tangent to the demand curve)
P > MC (not allocatively efficient — DWL exists)
P > minimum ATC (not productively efficient — excess capacity exists)
The firm produces at an output level BELOW the minimum ATC
Excess capacity: The firm could produce more at a lower average cost but chooses not to because MR would fall below MC.

Oligopoly

Characteristics

Few large firms dominating the market
Interdependent decisions (each firm's actions affect others)
High barriers to entry
Products can be homogeneous or differentiated
Strategic behavior (game theory)

Game Theory

Game theory analyzes strategic interactions where the outcome for each player depends on the actions of all players.

Payoff Matrix: A table showing each player's payoff (profit) for each combination of strategies.

Prisoner's Dilemma: The classic game theory example. Each player has a dominant strategy to act in their own self-interest, but the outcome is worse for both than if they had cooperated.

Dominant Strategy: A strategy that yields a higher payoff regardless of what the other player does.

Nash Equilibrium: A situation where no player can improve their payoff by unilaterally changing their strategy. Each player's strategy is optimal given the other's choice.

Case Study: Two gas stations (Exxon and Shell) deciding whether to charge high or low prices.

	Shell: High Price	Shell: Low Price
Exxon: High Price	Exxon: $100, Shell: $100	Exxon: $50, Shell: $150
Exxon: Low Price	Exxon: $150, Shell: $50	Exxon: $80, Shell: $80

Each firm's dominant strategy is to charge a low price (because $150 > $100 if the other charges high, and $80 > $50 if the other charges low)
Nash Equilibrium: Both charge low price, earning $80 each
This is worse than if both charged high ($100 each), but neither will unilaterally change because $80 > $50
Collusion would improve outcomes for both but is difficult to maintain (and often illegal)

Collusion

Cartel: A group of firms that act together like a monopoly to restrict output and raise prices. OPEC is the most famous example.
Collusion tends to break down because each firm has an incentive to cheat (produce more than agreed) to capture more profit.

Comparing Market Structures

Feature	Perfect Comp	Monopolistic Comp	Oligopoly	Monopoly
# of firms	Many	Many	Few	One
Product	Identical	Differentiated	Hom/Diff	Unique
Barriers	None	Low	High	Very High
Price maker/taker	Taker	Maker	Maker	Maker
P vs MC	P = MC	P > MC	P > MC	P > MC
LR profit	Zero	Zero	Can be > 0	> 0
DWL	None	Yes	Yes	Yes
Examples	Wheat, corn	Restaurants, clothing	Airlines, autos	Utilities, patents

Common Mistakes

Confusing the monopolist's MR and demand curves. MR is below demand (except for the first unit). MR has twice the slope of demand when demand is linear.
Thinking the monopolist's supply curve exists. A monopolist does not have a supply curve because the quantity produced depends on both MC and the shape of demand.
Confusing monopolistic competition's long-run equilibrium with perfect competition. Both have zero economic profit, but monopolistic competition is NOT efficient (P > MC, excess capacity).
Misidentifying Nash Equilibrium. It's where no player wants to change, NOT where the best joint outcome is.
Forgetting that monopolistic competition has excess capacity. The firm produces at a quantity less than the minimum ATC.

Self-Check Questions

A monopolist faces demand P = 100 - Q and has MC = 20 + Q. Calculate the profit-maximizing price and quantity.
Explain the three conditions necessary for a firm to practice price discrimination.
Why is there no supply curve for a monopoly?
In long-run monopolistic competition, why does the firm produce at a quantity below the minimum ATC? Explain using the firm's demand curve.
In the prisoner's dilemma, explain why the Nash equilibrium is not the socially optimal outcome.
Compare monopoly and perfect competition in terms of price, quantity, and efficiency.

Unit 5: Factor Markets

Key Topics

Derived demand
Marginal revenue product (MRP) and marginal product (MP)
Profit-maximizing hiring rule
Perfectly competitive labor markets
Monopsony
Cost-minimizing combination of resources

Derived Demand

The demand for factors of production (labor, capital, land) is derived from the demand for the goods and services those factors produce. If demand for cars increases, demand for autoworkers increases.

Key Concepts

Marginal Product (MP): The additional output from one more unit of labor.

Marginal Revenue Product (MRP): The additional revenue from hiring one more unit of labor. MRP = MP × MR

For a perfectly competitive firm in the product market, P = MR, so: MRP = MP × P (also called VMP — Value of the Marginal Product)

Marginal Resource Cost (MRC) (or Marginal Factor Cost, MFC): The additional cost of hiring one more unit of labor.

For a perfectly competitive firm in the factor market: MRC = Wage (W) (the firm can hire as many workers as it wants at the market wage)

Profit-Maximizing Hiring Rule

A firm maximizes profit by hiring labor up to the point where: MRP = MRC

Logic: If MRP > MRC, the firm gains more revenue than cost from hiring another worker, so it should hire more. If MRP < MRC, the last worker cost more than they produced, so the firm should hire fewer.

For a perfectly competitive firm (in both product and labor markets):

Hire until VMP = W (or MRP = W)

The firm's labor demand curve IS its MRP curve (the downward-sloping portion, below maximum MRP).

Perfectly Competitive Labor Market

Market Level

Labor demand: Sum of all individual firms' MRP curves (downward sloping)
Labor supply: Upward sloping (higher wage attracts more workers)
**Equilibrium wage (W)* determined by market supply and demand

Firm Level

The firm is a wage taker — it faces a horizontal labor supply curve at the market wage (W*)
The firm hires where MRP = W*
Labor supply = MRC = W* for the firm

Shifts in Labor Demand

Product demand increase → P↑ → MRP↑ → labor demand shifts right
Worker productivity increase → MP↑ → MRP↑ → labor demand shifts right
Price of a substitute input falls (e.g., automation becomes cheaper) → labor demand shifts left
Price of a complement input falls → labor demand shifts right

Shifts in Labor Supply

Changes in population, social norms, alternative opportunities, immigration

Monopsony

A monopsony is a market with a single buyer (employer) of labor.

Characteristics

One employer (or very few) dominating the labor market
The firm faces the upward-sloping market labor supply curve
MRC > Wage for all workers after the first (to hire more workers, the firm must raise the wage for ALL workers)
The MRC curve lies ABOVE the labor supply curve

Profit Maximization in Monopsony

Hire where MRP = MRC
Go DOWN to the labor supply curve to find the wage paid
The monopsony hires FEWER workers and pays a LOWER wage than a perfectly competitive labor market

Monopsony creates deadweight loss because it hires less than the socially optimal quantity of labor.

Case Study: A coal mining town with one employer. The mine is the only buyer of labor. To hire more miners, it must raise wages, but it must pay the higher wage to all miners. The MRC of each additional miner exceeds the wage.

Cost-Minimizing Rule

For a firm using multiple inputs (labor and capital), the cost-minimizing combination satisfies:

MPL / PL = MPK / PK

If MPL/PL > MPK/PK, the firm gets more output per dollar from labor and should hire more labor (and less capital) until the ratios are equal.

This is analogous to the utility-maximizing rule MUa/Pa = MUb/Pb.

Common Mistakes

Confusing MRP and demand. The MRP curve IS the labor demand curve for a perfectly competitive firm.
Thinking MRC = Wage in monopsony. In monopsony, MRC > Wage. MRC = Wage only in perfect competition.
Confusing the factor market and product market. Factor market: firm is a buyer of labor. Product market: firm is a seller of goods.
Forgetting that labor demand shifts with changes in product demand and productivity. Derived demand means anything affecting product demand or worker productivity shifts labor demand.

Self-Check Questions

A perfectly competitive firm sells output at $10 per unit. The marginal product of the 5th worker is 20 units. Calculate the MRP of the 5th worker.
Explain why the MRC curve lies above the labor supply curve in a monopsony.
If the market wage is $15 and a firm's MRP for the 10th worker is $18, should the firm hire the 10th worker? Explain.
How does an increase in the price of the firm's output affect its demand for labor? Explain.
Use the cost-minimizing rule to explain why a firm might substitute capital for labor when wages rise.
Compare the wage and employment level in a monopsony versus a perfectly competitive labor market.

Unit 6: Market Failure and the Role of Government

Key Topics

Externalities (negative and positive)
Public goods
Common resources (tragedy of the commons)
Asymmetric information
Income inequality
Government remedies for market failures

Market Failure

A market failure occurs when the free market fails to produce the allocatively efficient quantity of a good or service, resulting in a loss of total surplus (deadweight loss).

Types of Market Failure

Externalities
Public goods
Common resources
Imperfect competition (monopoly power)
Asymmetric information

Externalities

An externality is a cost or benefit that affects a third party who is not involved in the transaction.

Negative Externalities (Spillover Costs)

The social cost of production exceeds the private cost
MSC (Marginal Social Cost) = MPC + MEC (marginal external cost)
MSC > MPC (the supply curve reflects only MPC, not the full social cost)
The market overproduces relative to the socially optimal quantity
Deadweight loss results from producing units where MSC > MSB
Examples: Pollution, secondhand smoke, traffic congestion, noise

Government remedies:
Per-unit tax (Pigouvian tax): Set equal to the marginal external cost at the optimal quantity. Shifts the private supply curve up to align with MSC.
Regulation: Set limits on pollution levels or technology standards
Tradable pollution permits (cap and trade): The government sets a total cap on pollution and issues permits that firms can trade. Firms with low abatement costs reduce more and sell permits; firms with high abatement costs buy permits.
Lawsuits: Affected parties can sue for damages
Graphical analysis:
The market supply curve (MPC) is to the RIGHT of the MSC curve
Market equilibrium: where D = MPC (higher Q, lower P)
Socially optimal: where D = MSC (lower Q, higher P)
DWL is the triangle between MSC and demand, from Qoptimal to Qmarket

Positive Externalities (Spillover Benefits)

The social benefit of consumption exceeds the private benefit
MSB (Marginal Social Benefit) = MPB + MEB (marginal external benefit)
MSB > MPB (the demand curve reflects only MPB, not the full social benefit)
The market underproduces relative to the socially optimal quantity
Deadweight loss results from NOT producing units where MSB > MSC
Examples: Education, vaccinations, research and development, beekeeping (bees pollinate neighboring farms)

Government remedies:
Per-unit subsidy to consumers: Set equal to the marginal external benefit. Shifts demand right to align with MSB.
Per-unit subsidy to producers: Shifts supply right, lowering price and increasing quantity.
Government provision: The government directly provides the good (e.g., public education)
Regulation: Require consumption (e.g., mandatory vaccinations)

Public Goods

Types of Goods

	Excludable	Non-excludable
Rival	Private goods (food, clothing)	Common resources (fish in ocean, public pasture)
Non-rival	Club goods (cable TV, gym)	Public goods (national defense, streetlights)

Excludable: People can be prevented from consuming the good
Rival: One person's consumption reduces the amount available for others
Non-rival: One person's consumption does not reduce availability for others
Non-excludable: People cannot be prevented from consuming the good

Pure Public Goods

Both non-excludable and non-rival
Examples: national defense, streetlights, flood control, basic scientific research

The Free Rider Problem

Because public goods are non-excludable, individuals can benefit without paying
This leads to under-provision by private markets (firms can't charge for them)
Government must provide public goods and fund them through taxation

Common Resources (Tragedy of the Commons)

Rival but non-excludable
Each user consumes the resource for personal gain but shares the cost of depletion with everyone
Individual incentive to overuse → resource is depleted/destroyed
Examples: Overfishing, overgrazing, clean air, congested roads
Solutions:
Government regulation (fishing quotas, hunting seasons)
Privatization (making the resource excludable)
Tradable permits

Asymmetric Information

Occurs when one party in a transaction has more information than the other.

Adverse Selection

Occurs BEFORE the transaction
The party with more information exploits the information advantage
Example: Used car market (lemons problem). Sellers know the quality of their car; buyers don't. Low-quality cars ("lemons") drive high-quality cars out of the market.
Example: Health insurance. Unhealthy people are more likely to buy insurance, raising premiums and driving healthy people away.

Moral Hazard

Occurs AFTER the transaction
One party changes behavior because they're protected from risk
Example: A person with car insurance drives more recklessly.
Example: Bank bailouts encourage excessive risk-taking.
Government remedies:
Disclosure requirements, regulations, warranties, health inspections, insurance mandates

Income Inequality

Measuring Inequality

Lorenz Curve: A graph showing the cumulative share of income received by cumulative portions of the population.

The line of perfect equality is a 45-degree line
The Lorenz curve bows below it
The further the Lorenz curve is from the 45-degree line, the greater the inequality
Gini Coefficient: Ratio of the area between the line of perfect equality and the Lorenz curve to the total area under the line of perfect equality.
Ranges from 0 (perfect equality) to 1 (perfect inequality)

Government Policies to Address Inequality

Progressive taxation: Higher tax rates on higher incomes
Transfer payments: Welfare, Social Security, unemployment insurance
In-kind transfers: Food stamps, Medicaid, housing assistance
Minimum wage laws: Can create surplus (unemployment) but may reduce poverty
Education and training programs: Increase human capital

Equity-Efficiency Tradeoff

Policies that promote equity (redistribution) may reduce economic efficiency. Higher taxes may discourage work and investment. This tradeoff is a fundamental challenge for policymakers.

Common Mistakes

Confusing negative and positive externalities. Negative = overproduce (tax it). Positive = underproduce (subsidize it).
Shifting the wrong curve for externalities. For a negative production externality, the supply curve (MPC) needs to shift LEFT to MSC. For a positive consumption externality, the demand curve (MPB) needs to shift RIGHT to MSB.
Confusing public goods with common resources. Public goods = non-rival, non-excludable (under-produced). Common resources = rival, non-excludable (over-used).
Confusing adverse selection and moral hazard. Adverse selection = before transaction (hidden information). Moral hazard = after transaction (changed behavior).
Forgetting to show the DWL on externality graphs. DWL is between the MSC and MSB (or demand) curves, from the optimal quantity to the market quantity.

Self-Check Questions

Draw a graph showing a negative production externality. Label the market equilibrium, socially optimal quantity, and the deadweight loss.
Explain the difference between a public good and a common resource. Provide an example of each.
A factory pollutes a river, causing harm to downstream fishermen. Explain how a per-unit tax on the factory could lead to the socially optimal level of production.
Why does the free rider problem prevent private markets from providing public goods efficiently?
Explain the difference between adverse selection and moral hazard. Give an example of each.
A vaccine has a positive externality because it reduces the spread of disease. Explain whether a subsidy to consumers or producers would be more effective, or if they are equivalent.

Practice sets

Unit 1 Practice: Basic Economic Concepts

1. Which of the following best describes opportunity cost?

(A) The total cost of all alternatives given up
(B) The value of the next best alternative given up
(C) The monetary cost of a decision
(D) The time spent making a decision

Answer: B. Opportunity cost is only the NEXT BEST alternative, not the sum of all alternatives. Answer: B. OC of 1 steel = 200/100 = 2 wheat. Answer: C. Economic growth shifts the PPC outward (more resources or better technology). Answer: B. Rational decision-making uses marginal analysis: take the action if MB > MC, until MB = MC.

2. A country can produce 100 units of steel or 200 units of wheat. What is the opportunity cost of 1 unit of steel?

(A) 0.5 wheat
(B) 2 wheat
(C) 100 wheat
(D) 200 wheat

Answer: B. OC of 1 steel = 200/100 = 2 wheat. Answer: C. Economic growth shifts the PPC outward (more resources or better technology). Answer: B. Rational decision-making uses marginal analysis: take the action if MB > MC, until MB = MC.

3. Economic growth would be represented on a PPC as:

(A) A movement from a point inside the curve to a point on the curve
(B) A movement along the curve
(C) An outward shift of the entire curve
(D) An inward shift of the entire curve

Answer: C. Economic growth shifts the PPC outward (more resources or better technology). Answer: B. Rational decision-making uses marginal analysis: take the action if MB > MC, until MB = MC.

4. A rational decision maker should take an action if:

(A) The total benefit exceeds the total cost
(B) The marginal benefit exceeds the marginal cost
(C) The marginal cost is zero
(D) The opportunity cost is positive

Answer: B. Rational decision-making uses marginal analysis: take the action if MB > MC, until MB = MC.

Free-Response Question

Country Alpha can produce 40 bushels of corn or 20 bushels of soybeans using all its resources. Country Beta can produce 30 bushels of corn or 30 bushels of soybeans using all its resources.

a. Calculate the opportunity cost of producing 1 bushel of corn in each country.

b. Which country has a comparative advantage in corn? In soybeans? Explain.

c. If the terms of trade are 1 corn for 1.25 soybeans, will both countries benefit from trade? Explain.

Scoring Guidelines

Part (a):

Alpha: OC of 1 corn = 20/40 = 0.5 soybeans
Beta: OC of 1 corn = 30/30 = 1 soybean
Part (b):
Alpha has a comparative advantage in corn (0.5 < 1)
Beta has a comparative advantage in soybeans (Alpha's OC of 1 soybean = 40/20 = 2 corn; Beta's OC of 1 soybean = 30/30 = 1 corn; Beta has the lower OC)
Part (c):
Yes. The terms of trade (1 corn for 1.25 soybeans) falls between Alpha's cost of corn (0.5 soybeans) and Beta's cost of corn (1 soybean). Alpha gets 1.25 soybeans per corn (better than its domestic 0.5). Beta gives up 1.25 soybeans for 1 corn (better than its domestic 1 soybean per corn).

AP Microeconomics — Practice Problems: Unit 2

Section A: Demand and Supply Determinants

1. Which of the following will increase the demand for smartphones?

(A) A decrease in the price of smartphones
(B) An increase in the price of phone cases (a complementary good)
(C) A decrease in consumer income, assuming smartphones are a normal good
(D) A new study showing that prolonged screen time improves cognitive function
(E) An increase in the price of tablets (a substitute good)
Answer: E. An increase in the price of a substitute good (tablets) shifts the demand curve for smartphones to the right (increase in demand). Option A is a movement along the curve, not a shift. Option B: phone cases are complementary, so a higher price of cases would decrease demand for smartphones. Option C: lower income decreases demand for a normal good. Option D is tempting, but we treat this as an increase in consumer tastes/preferences, which would increase demand — however, E is more directly and unambiguously correct because it relies on the well-established substitute-good relationship.

2. A technological breakthrough reduces the cost of producing electric vehicles. What happens in the market for electric vehicles?
(A) Demand increases, equilibrium price rises, equilibrium quantity rises.
(B) Supply increases, equilibrium price falls, equilibrium quantity rises.
(C) Supply decreases, equilibrium price rises, equilibrium quantity falls.
(D) Demand decreases, equilibrium price falls, equilibrium quantity falls.
(E) Both supply and demand increase, equilibrium price is ambiguous, quantity rises.
Answer: B. A reduction in production costs shifts the supply curve to the right (increase in supply). The new equilibrium has a lower price and higher quantity. Demand does not shift in this scenario.

3. If both demand and supply increase simultaneously, which of the following is definitely true?
(A) Equilibrium price rises.
(B) Equilibrium price falls.
(C) Equilibrium quantity rises.
(D) Equilibrium quantity falls.
(E) Equilibrium price stays the same.
Answer: C. An increase in demand raises both P and Q. An increase in supply lowers P and raises Q. The combined effect on price is ambiguous (depends on which shift is larger), but quantity unambiguously increases.

Section B: Price Elasticity of Demand

4. When the price of a good increases from $8 to $10, the quantity demanded decreases from 100 units to 80 units. Using the midpoint method, calculate the price elasticity of demand.

Solution:

% change in quantity = (80 − 100) / ((80 + 100)/2) = (−20) / 90 = −22.22%
% change in price = (10 − 8) / ((10 + 8)/2) = 2 / 9 = 22.22%
Ed = |−22.22% / 22.22%| = 1.0 (unit elastic)
5. If the price elasticity of demand for a good is 0.3, which of the following is true?
(A) The good is a luxury.
(B) Total revenue moves in the same direction as the price change.
(C) Total revenue moves in the opposite direction as the price change.
(D) The demand curve is perfectly elastic.
(E) Consumers are very sensitive to price changes.
Answer: B. An elasticity of 0.3 is inelastic (Ed < 1). With inelastic demand, total revenue moves in the same direction as the price change. If price increases, TR increases. If price decreases, TR decreases.

6. At a price of $5, a firm sells 200 units. At $7, it sells 140 units. What happens to total revenue as price rises from $5 to $7?

Solution:
TR at $5 = 5 × 200 = $1,000
TR at $7 = 7 × 140 = $980
Total revenue decreased from $1,000 to $980.
Since TR fell when price increased, demand is elastic in this range (confirming Ed > 1). Using the midpoint method: Ed = |−35.29% / 33.33%| ≈ 1.06.

Section C: Cross-Price and Income Elasticity

7. When the price of coffee rises by 10%, the quantity demanded of tea increases by 5%. What is the cross-price elasticity? What is the relationship between coffee and tea?

Solution:

Ecross = (%Δ Qd of tea) / (%Δ P of coffee) = 5% / 10% = +0.5
Positive cross-price elasticity → coffee and tea are substitute goods. (If it were negative, they'd be complements.)
8. When consumer income rises by 8%, the quantity demanded of used clothing decreases by 4%. What is the income elasticity? What type of good is used clothing?

Solution:
Eincome = (%Δ Qd) / (%Δ Income) = −4% / 8% = −0.5
Negative income elasticity → used clothing is an inferior good. As income rises, people buy less of it.

Section D: Consumer and Producer Surplus

9. The demand curve is given by P = 50 − 2Q and the supply curve is P = 10 + Q. Calculate consumer surplus and producer surplus at equilibrium.

Solution:

Equilibrium: 50 − 2Q = 10 + Q → 3Q = 40 → Q = 40/3 ≈ 13.33
P = 50 − 2(40/3) = 50 − 80/3 = 70/3 ≈ $23.33
Consumer Surplus = ½ × (50 − 23.33) × 13.33 = ½ × 26.67 × 13.33 ≈ $177.78
Producer Surplus = ½ × (23.33 − 10) × 13.33 = ½ × 13.33 × 13.33 ≈ $88.84
10. A price ceiling is set at $15 in the market described above. Is it binding? What happens to total surplus?

Solution:
Equilibrium price is $23.33. A ceiling at $15 is below equilibrium → binding price ceiling.
At P = $15: Qd = (50 − 15)/2 = 17.5; Qs = 15 − 10 = 5. Quantity traded = 5 units (the lower of Qd and Qs).
New CS = ½ × (50 − 15) × 5 + ½ × (35 − 15) × 5 = 87.5 + 50 = $137.50 (wait — need to use the triangle + rectangle correctly)
- CS = ½ × (50 − 15) × 5 = $87.50
New PS = ½ × (15 − 10) × 5 = $12.50
New total surplus = $87.50 + $12.50 = $100.00
Deadweight loss = $177.78 + $88.84 − $100.00 ≈ $166.62
The price ceiling creates a shortage (17.5 demanded vs. 5 supplied) and substantial deadweight loss.

Section E: Tax Incidence and Deadweight Loss

11. The government imposes a $4 per-unit tax on sellers in a market where demand is P = 100 − Q and supply is P = 20 + Q. Calculate:

(a) The new equilibrium quantity after the tax
(b) The price paid by buyers
(c) The price received by sellers (net of tax)
(d) The tax incidence on buyers and sellers
(e) The deadweight loss
Solution:
Original equilibrium: 100 − Q = 20 + Q → Q = 40, P = $60.
With tax on sellers: supply shifts up by $4. New supply: P = 24 + Q.
New equilibrium: 100 − Q = 24 + Q → 2Q = 76 → Q = 38
Pb (price buyers pay) = 100 − 38 = $62
Ps (price sellers keep) = 62 − 4 = $58 (or Ps = 24 + 38 = 62... wait: 20 + 38 = 58 ✓)
Tax burden on buyers = 62 − 60 = $2; Tax burden on sellers = 60 − 58 = $2.
DWL = ½ × tax × ΔQ = ½ × $4 × (40 − 38) = ½ × 4 × 2 = $4

Section F: Price Controls

12. A binding price floor is set above the equilibrium price. Which of the following will result?

(A) A shortage of the good
(B) An increase in the quantity demanded
(C) A surplus of the good
(D) An increase in consumer surplus
(E) Market equilibrium is maintained
Answer: C. A binding price floor set above equilibrium creates a surplus (excess supply). Quantity supplied exceeds quantity demanded.

Self-Check Quiz

If demand is perfectly inelastic, a price increase will cause total revenue to ___. (increase / decrease / stay the same)
If two goods have a cross-price elasticity of −2.5, they are ___. (substitutes / complements)
A per-unit tax on a good with perfectly inelastic demand creates ___ deadweight loss. (zero / positive / infinite)
When a tax is levied on sellers, the equilibrium price ___. (rises by the full amount of the tax / rises by less than the full tax / stays the same)
If Ed = 0.8 and price falls by 5%, quantity demanded will rise by approximately ___. (4% / 6% / 5%)
Consumer surplus is the area ___ the demand curve and ___ the market price. (above / below)
Answers: 1. Increase. 2. Complements (negative cross-price elasticity). 3. Zero (no deadweight loss when demand is perfectly inelastic). 4. Rises by less than the full tax (sellers bear part of the burden). 5. 4% (0.8 × 5% = 4%). 6. Below; above.

AP Microeconomics — Practice Problems: Unit 3

Section A: Production Functions

1. A firm has the following short-run production data (labor is the variable input; capital is fixed):

Labor (L)	Total Product (TP)
0	0
1	10
2	25
3	45
4	60
5	70
6	75
7	72

Calculate the Marginal Product (MP) of each worker and identify:

(a) Where increasing marginal returns occur
(b) Where diminishing marginal returns begin
(c) Where negative marginal returns begin
Solution:

| L | TP | MP = ΔTP/ΔL | |----|-----|-------------| | 0 | 0 | — | | 1 | 10 | 10 | | 2 | 25 | 15 | | 3 | 45 | 20 | | 4 | 60 | 15 | | 5 | 70 | 10 | | 6 | 75 | 5 | | 7 | 72 | −3 |
(a) Increasing marginal returns: Workers 1 to 3 (MP rises from 10 → 15 → 20). Each additional worker adds more output than the last.
(b) Diminishing marginal returns begin at L = 4 (MP drops from 20 to 15). The 4th worker adds less than the 3rd worker.
(c) Negative marginal returns begin at L = 7 (MP = −3). The 7th worker actually reduces total output.

Section B: Short-Run Costs

2. Given the following information, complete the cost table:

Total Fixed Cost (TFC) = $100 at all levels of output
Total Variable Cost (TVC) data: Q=0: $0, Q=1: $60, Q=2: $100, Q=3: $140, Q=4: $200, Q=5: $300
| Q | TFC | TVC | TC | AFC | AVC | ATC | MC | |----|-----|-----|------|-----|-----|-----|-----| | 0 | 100 | 0 | 100 | — | — | — | — | | 1 | 100 | 60 | 160 | 100 | 60 | 160 | 60 | | 2 | 100 | 100 | 200 | 50 | 50 | 100 | 40 | | 3 | 100 | 140 | 240 | 33 | 47 | 80 | 40 | | 4 | 100 | 200 | 300 | 25 | 50 | 75 | 60 | | 5 | 100 | 300 | 400 | 20 | 60 | 80 | 100 |

Key observations:
MC initially falls (60 → 40 → 40) due to increasing returns, then rises (60 → 100) due to diminishing returns.
ATC is minimized at Q = 4 ($75) — this is the productively efficient output in the short run.
MC intersects both AVC and ATC at their minimum points.
MC = AVC = $47 at approximately Q = 2.7 (shutdown point approximation); MC = ATC = $75 at Q = 4 (breakeven point).
3. Which of the following statements about short-run costs is correct?
(A) AFC increases as output increases.
(B) MC intersects ATC at its minimum point.
(C) ATC always equals AVC + MC.
(D) TC equals VC at zero output.
(E) The law of diminishing returns explains why AFC is U-shaped.
Answer: B. MC intersects ATC (and AVC) at their respective minimum points. This is a fundamental relationship. Option A is wrong: AFC decreases as output increases. Option C is wrong: ATC = AFC + AVC, not AVC + MC. Option D is wrong: TC = FC at zero output. Option E is wrong: AFC decreases continuously; the U-shape of ATC is due to diminishing returns affecting AVC.

Section C: Long-Run Costs and Economies of Scale

4. As a firm increases its plant size from small to medium to large, its long-run average total cost (LRATC) decreases from $20 to $15 to $18 per unit. Describe the cost conditions at each plant size.

Solution:

Small to Medium: LRATC falls from $20 to $15. This indicates economies of scale — the firm becomes more efficient as it grows.
Medium to Large: LRATC rises from $15 to $18. This indicates diseconomies of scale — the firm becomes less efficient, likely due to coordination problems, bureaucratic inefficiencies, or management challenges at larger scale.
The minimum efficient scale is at the medium plant size ($15 per unit), where LRATC is lowest.
5. Which of the following is a source of economies of scale?
(A) The law of diminishing marginal returns
(B) Increased specialization of labor and management
(C) Rising input prices as the firm expands
(D) A binding price ceiling
(E) The shutdown rule
Answer: B. Specialization of labor allows workers to focus on specific tasks, increasing productivity and lowering average costs. This is a key source of economies of scale.

Section D: Profit Maximization (MR = MC)

6. A perfectly competitive firm faces a market price of $20. Its total costs are given by TC = 100 + 10Q + Q².

(a) What is the profit-maximizing output?
(b) Calculate total profit at that output.
(c) Should the firm produce or shut down in the short run?
(d) Should the firm stay in the industry in the long run?
Solution:
MC = dTC/dQ = 10 + 2Q
Set MR = MC: 20 = 10 + 2Q → 10 = 2Q → Q = 5
TR = 20 × 5 = $100
TC = 100 + 10(5) + 5² = 100 + 50 + 25 = $175
Profit = $100 − $175 = −$75 (economic loss of $75)
Shutdown decision: AVC at Q=5: TVC/Q = (10Q + Q²)/Q = 10 + Q = 10 + 5 = $15. Since P ($20) > AVC ($15), the firm should produce in the short run. It loses less by producing ($75 loss) than by shutting down (which would lose all FC = $100).
Long-run decision: Since P ($20) < ATC at Q=5 ($175/5 = $35), the firm has an economic loss and should exit the industry in the long run.

Section E: Perfect Competition

7. Which of the following is NOT a characteristic of a perfectly competitive market?

(A) Many buyers and sellers
(B) Firms sell identical (homogeneous) products
(C) Firms are price takers
(D) Barriers to entry
(E) Perfect information
Answer: D. Perfect competition assumes NO barriers to entry or exit. Free entry and exit ensure that firms earn zero economic profit in the long run.

8. In a perfectly competitive market, the firm's demand curve is:
(A) Downward sloping
(B) Upward sloping
(C) Perfectly elastic (horizontal) at the market price
(D) The same as the market demand curve
(E) Kinked at the current price
Answer: C. Each individual firm faces a perfectly elastic (horizontal) demand curve at the market price. The firm is a price taker and can sell any quantity at that price.

9. A perfectly competitive industry is in long-run equilibrium. Consumer incomes rise and the good is normal. Describe the adjustment process to the new long-run equilibrium.

Solution:
Short-run: Higher incomes increase demand → demand shifts right → market price rises → each firm's MR rises → firms produce more (moving up MC curve) → firms earn positive economic profit.
Long-run adjustment: Positive economic profits attract new firms to enter the industry → market supply shifts right → price falls back toward minimum ATC → profits shrink to zero.
New long-run equilibrium: Price returns to minimum ATC (zero economic profit), but at a higher industry output with more firms. Each firm still produces at the efficient scale.

Section F: Efficiency

10. Define and explain the two types of efficiency achieved in a perfectly competitive long-run equilibrium.

Solution:

Allocative Efficiency (P = MC): The market produces the quantity where the marginal benefit to consumers (price they're willing to pay) equals the marginal cost of production. This ensures resources are allocated to produce the goods society values most. P = MC is the condition.
Productive Efficiency (P = minimum ATC): Each firm produces at the lowest possible per-unit cost. This occurs when P = minimum ATC. No resources are wasted.
In perfect competition long-run equilibrium, both P = MC and P = min ATC are achieved simultaneously, meaning the market is both allocatively and productively efficient.

Self-Check Quiz

The law of diminishing marginal returns explains why MC eventually ___. (rises / falls / stays constant)
In the short run, a firm should shut down if price is less than ___. (AFC / AVC / ATC)
A perfectly competitive firm earns ___ economic profit in long-run equilibrium. (positive / zero / negative)
If TC = 200 + 5Q + 0.5Q² and P = $15, the profit-maximizing output is ___. (Q = 10 / Q = 15 / Q = 5)
Economies of scale occur when LRATC ___ as output increases. (rises / falls / stays constant)
MC intersects AVC at the ___ point and ATC at the ___ point. (shutdown / breakeven)
Answers: 1. Rises. 2. AVC (the shutdown rule: shut down if P < AVC). 3. Zero. 4. Q = 10 (MC = 5 + Q = 15 → Q = 10). 5. Falls. 6. Shutdown; breakeven.

AP Microeconomics — Practice Problems: Unit 4

Section A: Monopoly Basics

1. Which of the following is a characteristic of monopoly?

(A) Many sellers
(B) Price-taking behavior
(C) Barriers to entry
(D) Perfect information
(E) Homogeneous products
Answer: C. A monopoly is a single seller facing the entire market demand, protected by barriers to entry (legal, natural, or strategic). All other options describe perfect competition.

2. A monopolist faces the demand curve P = 100 − 2Q and has total cost TC = 50 + 10Q + Q². Calculate:
(a) The profit-maximizing output and price
(b) Total revenue, total cost, and economic profit
(c) The deadweight loss compared to a perfectly competitive outcome
Solution:
MR = 100 − 4Q (MR has twice the slope of demand for linear demand)
MC = dTC/dQ = 10 + 2Q
Set MR = MC: 100 − 4Q = 10 + 2Q → 90 = 6Q → Q = 15
P = 100 − 2(15) = $70
TR = 70 × 15 = $1,050
TC = 50 + 10(15) + 15² = 50 + 150 + 225 = $425
Profit = $1,050 − $425 = $625
Deadweight loss:
Under perfect competition: P = MC → 100 − 2Q = 10 + 2Q → Q = 22.5, P = $55
DWL = ½ × (Pmonopoly − Pcompetitive) × (Qcompetitive − Qmonopoly)
DWL = ½ × (70 − 55) × (22.5 − 15) = ½ × 15 × 7.5 = $56.25
3. A natural monopoly exists when:
(A) One firm controls all natural resources
(B) A single firm can supply the entire market at a lower cost than two or more firms due to economies of scale
(C) The government grants an exclusive franchise
(D) A firm holds a patent on a product
(E) There are high fixed costs and low variable costs such that ATC declines over the entire range of market demand
Answer: B (or E — both describe aspects of natural monopoly, but B is the defining economic condition). A natural monopoly occurs when one firm's LRATC declines over the entire market output range, making it more efficient for one firm to serve the market.

Section B: Monopoly Profit Maximization and Efficiency

4. Why does a monopoly cause allocative inefficiency?

(A) P > MC, meaning the monopolist produces less than the socially optimal quantity
(B) The monopolist produces where ATC is minimized
(C) Consumer surplus is maximized
(D) The monopolist faces a perfectly elastic demand curve
(E) Producer surplus is minimized
Answer: A. The monopolist produces where MR = MC, but charges a price on the demand curve above MC. This means some units where MB > MC are not produced, creating deadweight loss. The monopolist underproduces relative to the socially optimal level.

5. Government regulators want to set price for a natural monopoly. If they set price equal to marginal cost:
(A) The monopolist earns a positive economic profit
(B) The monopolist earns zero economic profit
(C) The monopolist suffers a loss (P < ATC)
(D) The monopolist produces the monopoly profit-maximizing quantity
(E) Deadweight loss increases
Answer: C. Setting P = MC achieves allocative efficiency but since MC < ATC (due to economies of scale), the firm cannot cover its costs and would need a subsidy to stay in business. This is a practical challenge of regulating natural monopolies.

Section C: Price Discrimination

6. A movie theater charges $12 for adult tickets and $7 for student tickets. What condition must hold for this to be an example of successful price discrimination?

(A) Students have less elastic demand than adults
(B) The theater can prevent resale between markets
(C) The theater is a price taker
(D) Both markets have identical demand curves
(E) Adults and students have identical willingness to pay
Answer: B. The key requirements for price discrimination are: (1) market power, (2) ability to identify different groups with different elasticities, and (3) ability to prevent resale. Students typically have more elastic demand (they're more price-sensitive), and the theater must be able to prevent students from buying tickets for adults.

7. Under perfect (first-degree) price discrimination:
(A) The monopolist charges the same price to all consumers
(B) Consumer surplus is zero and all surplus goes to the producer
(C) Deadweight loss increases compared to single-price monopoly
(D) Output is less than under single-price monopoly
(E) The monopolist earns normal profit
Answer: B. Perfect price discrimination charges each consumer their maximum willingness to pay. This eliminates all consumer surplus (CS = 0), maximizes producer surplus, and interestingly produces the competitive output level (P = MC for the last unit), eliminating deadweight loss. Total surplus is maximized, but distribution is extremely unequal.

Section D: Monopolistic Competition

8. Which of the following is true in a monopolistically competitive market?

(A) Firms produce identical products
(B) There are significant barriers to entry
(C) In the long run, firms earn zero economic profit
(D) Firms are price takers
(E) The demand curve is perfectly elastic
Answer: C. Like perfect competition, monopolistic competition has free entry and exit, so long-run economic profit is zero. But unlike perfect competition, firms sell differentiated products and face downward-sloping demand curves.

9. A monopolistically competitive firm is shown in long-run equilibrium. Which of the following is true?
(A) P = MC
(B) P = minimum ATC
(C) P > MC and P > minimum ATC
(D) P = MC but P < minimum ATC
(E) The firm has excess capacity but is productively efficient
Answer: C. In long-run equilibrium, the monopolistically competitive firm:
Produces where MR = MC (so P > MC, causing allocative inefficiency)
Earns zero profit (P = ATC, but not at the minimum of ATC)
Has excess capacity (produces less than the output that minimizes ATC)
Is NOT productively efficient

Section E: Oligopoly and Game Theory

10. Two firms (A and B) are deciding whether to advertise or not advertise. Their payoffs (profits) are shown below:

	Firm B: Advertise	Firm B: Not Advertise
Firm A: Advertise	$50, $50	$100, $20
Firm A: Not Advertise	$20, $100	$80, $80

(a) What is the dominant strategy for each firm?
(b) What is the Nash equilibrium?
(c) Is this a prisoner's dilemma? Explain.
Solution:
(a) Firm A's perspective: If B advertises, A earns $50 (advertise) vs. $20 (not) → advertise. If B doesn't advertise, A earns $100 (advertise) vs. $80 (not) → advertise. Advertise is dominant for A.
Firm B's perspective: If A advertises, B earns $50 (advertise) vs. $20 (not) → advertise. If A doesn't advertise, B earns $100 (advertise) vs. $80 (not) → advertise. Advertise is dominant for B.
(b) Nash equilibrium: Both firms advertise, earning ($50, $50).
(c) Yes, this is a prisoner's dilemma. Both firms would be better off if neither advertised ($80, $80), but each has an individual incentive to advertise. Self-interested behavior leads to a suboptimal outcome.
11. In an oligopoly with a kinked demand curve model:
(A) Price increases always lead to large quantity increases
(B) Price decreases are matched by rivals, but price increases are not
(C) The demand curve is perfectly elastic at the kink
(D) Firms always collude successfully
(E) MR is undefined at the kink, leading to a gap in the MR curve
Answer: E. The kinked demand curve model assumes rivals match price decreases but not price increases. This creates a kink in the demand curve at the current price, which causes a gap (vertical segment) in the MR curve. This gap means small changes in MC may not lead to price changes, explaining price rigidity in oligopolies.

12. A cartel is most likely to break down because:
(A) All firms in the cartel earn positive economic profit
(B) Each individual firm has an incentive to cheat by producing more than the agreed quota
(C) The cartel sets prices too low
(D) Consumers refuse to buy from cartel members
(E) Governments always enforce cartel agreements
Answer: B. Cartels are inherently unstable because if all firms restrict output and raise prices, each individual firm has a strong incentive to secretly increase production and earn more profit by selling at the cartel price. As firms cheat, total output rises, price falls, and the cartel collapses.

Self-Check Quiz

A monopoly produces where ___ = ___ and charges the price on the ___. (MR; MC; demand curve)
Compared to a perfectly competitive market, a monopoly results in ___ consumer surplus and ___ deadweight loss. (higher / lower)
In the long run, a monopolistically competitive firm earns ___ economic profit and produces with ___ capacity. (positive / zero / negative; excess / no)
A Nash equilibrium occurs when each player's strategy is ___ given the strategies of others. (optimal / dominant / random)
In a kinked demand curve model, rivals are assumed to match ___ decreases but not ___ increases. (price / quantity)
Price discrimination converts ___ surplus into ___ surplus. (consumer; producer)
Answers: 1. MR; MC; demand curve. 2. Lower; positive (or higher deadweight loss). 3. Zero; excess. 4. Optimal (a best response). 5. Price; price. 6. Consumer; producer.

AP Microeconomics — Practice Problems: Unit 5

Section A: Factor Demand — MRP and MRC

1. A perfectly competitive firm sells its output for $10 per unit. The marginal product of the 3rd worker is 20 units, and the marginal product of the 4th worker is 15 units. Each worker is paid $120 per day. How many workers should the firm hire?

Solution:

MRP of 3rd worker = MP × P = 20 × $10 = $200
MRP of 4th worker = MP × P = 15 × $10 = $150
MRC (wage) = $120 per worker
Hire 3rd worker: $200 > $120 → Yes, hire
Hire 4th worker: $150 > $120 → Yes, hire
MRP of 5th worker = 10 × $10 = $100 < $120 → No, stop here
The firm should hire 4 workers (continue hiring as long as MRP ≥ MRC).

2. A firm in a perfectly competitive labor market faces a wage rate of $50. Its MRP schedule is:

| Workers | MRP | |---------|-----| | 1 | $80 | | 2 | $70 | | 3 | $60 | | 4 | $50 | | 5 | $40 |

How many workers will the firm hire? What is the total labor cost?

Solution:
Hire as long as MRP ≥ wage ($50):
- Worker 1: $80 ≥ $50 → Hire
- Worker 2: $70 ≥ $50 → Hire
- Worker 3: $60 ≥ $50 → Hire
- Worker 4: $50 ≥ $50 → Hire (MRP = MRC at the margin)
- Worker 5: $40 < $50 → Stop
Hire 4 workers.
Total labor cost = 4 × $50 = $200
3. The demand curve for labor is:
(A) The same as the firm's output demand curve
(B) The MRP curve (downward sloping due to diminishing marginal returns)
(C) Perfectly elastic in all market structures
(D) Upward sloping because of the law of supply
(E) Independent of the product market
Answer: B. The derived demand for labor comes from the MRP schedule. MRP = MP × MR. Since MP declines due to diminishing returns, MRP declines, creating a downward-sloping labor demand curve.

Section B: Shifts in Factor Demand

4. Which of the following will shift the demand curve for labor to the RIGHT?

(A) A decrease in the price of the firm's output
(B) An increase in the wage rate
(C) An increase in the marginal productivity of labor (due to better technology)
(D) A decrease in the price of a substitute input
(E) A decrease in the number of firms in the industry
Answer: C. Better technology increases the marginal product of labor, which increases MRP (= MP × MR), shifting the labor demand curve to the right. Option A decreases MRP (shifts left). Option B causes movement along the labor demand curve. Option D may shift labor demand left if substitute becomes cheaper. Option E shifts the market labor demand left.

5. A bakery uses both ovens (capital) and bakers (labor). If the price of ovens decreases significantly, what will happen to the demand for bakers in the short run vs. the long run?

Solution:
Short run (substitution effect): Lower oven prices make capital relatively cheaper. The bakery substitutes toward capital and away from labor → demand for bakers decreases.
Long run (scale effect): Lower costs of production mean the bakery can expand output. As output expands, the demand for all inputs (including labor) increases → demand for bakers increases.
Net effect: Ambiguous in theory, but the scale effect often dominates in the long run for a normal input. On the AP exam, be prepared to discuss both effects.

Section C: Perfectly Competitive Labor Market

6. In a perfectly competitive labor market:

(A) Each firm faces a downward-sloping labor supply curve
(B) The market wage is determined by the intersection of market labor supply and market labor demand
(C) Firms can influence the wage rate
(D) Workers have significant bargaining power
(E) There is only one employer of labor
Answer: B. In a perfectly competitive labor market, the market wage is determined by the intersection of market labor demand (sum of all firms' MRP curves) and market labor supply. Individual firms are wage takers and face a perfectly elastic (horizontal) labor supply curve at the market wage.

7. A perfectly competitive labor market has:
Market labor demand: w = 200 − 4L (where w = wage, L = number of workers in thousands)
Market labor supply: w = 40 + L
Calculate:
(a) The equilibrium wage and employment level
(b) Total labor income
Solution:
200 − 4L = 40 + L → 160 = 5L → L = 32 (thousand workers)
w = 40 + 32 = $72
Total labor income = 32 × 72 = $2,304 (thousand)

Section D: Monopsony

8. A monopsony is:

(A) A market with a single seller of a good
(B) A market with a single buyer of a good or resource
(C) A market with many buyers and sellers
(D) A labor union that controls all workers
(E) A government-regulated labor market
Answer: B. A monopsony is a market with a single buyer (or dominant buyer). In factor markets, a monopsony is a single employer of labor (e.g., a company town, a specialized industry in a small city).

9. A monopsony faces the labor supply schedule:

| Wage (w) | Workers willing to work (L) | Total Labor Cost (TLC) | Marginal Resource Cost (MRC) | |----------|---------------------------|----------------------|---------------------------| | $10 | 1 | $10 | $10 | | $12 | 2 | $24 | $14 | | $15 | 3 | $45 | $21 | | $19 | 4 | $76 | $31 | | $24 | 5 | $120 | $44 |

If the MRP of the 3rd worker is $25 and the MRP of the 4th worker is $20, how many workers will the monopsony hire?

Solution:
The monopsony hires where MRP = MRC.
At L=2: MRC = $14, hire 2nd worker (MRP > $14)
At L=3: MRC = $21. If MRP of 3rd worker = $25 > $21, hire the 3rd worker.
At L=4: MRC = $31. If MRP of 4th worker = $20 < $31, do NOT hire the 4th worker.
Hire 3 workers at a wage of $15.
Key insight: The monopsony pays the wage from the supply curve ($15), not the MRC. The MRC exceeds the wage because hiring an additional worker requires raising the wage for ALL workers. The monopsony exploits this wedge — it hires fewer workers and pays a lower wage than a perfectly competitive labor market would.

Section E: Cost-Minimizing Combination of Resources

10. A firm uses labor (L) and capital (K). The marginal product of labor is 40 units, and the marginal product of capital is 60 units. The price of labor (w) is $20 per hour, and the price of capital (r) is $30 per hour. Is the firm minimizing costs? If not, what should it do?

Solution:

Check the cost-minimizing condition: MPL/w = MPK/r
MPL/w = 40/$20 = 2
MPK/r = 60/$30 = 2
Since 2 = 2, the firm is minimizing costs. The marginal product per dollar spent is equal across both inputs.
11. Now suppose MPL = 30, MPK = 60, w = $10, r = $30. Is the firm minimizing costs?

Solution:
MPL/w = 30/10 = 3
MPK/r = 60/30 = 2
Since MPL/w (3) > MPK/r (2), the firm is not minimizing costs.
The firm gets more "bang for the buck" from labor than from capital. It should hire more labor and less capital until the ratios equalize.

Self-Check Quiz

MRP equals ___ × ___. (Marginal product; marginal revenue)
A firm should continue hiring workers as long as ___ ≥ ___. (MRP; MRC)
In a perfectly competitive labor market, the firm faces a ___ (horizontal/upward-sloping/downward-sloping) labor supply curve.
In a monopsony, MRC is ___ (greater than / equal to / less than) the wage rate.
The cost-minimizing combination of resources occurs where MPL/w ___ MPK/r. (= / > / <)
Derived demand means that demand for labor depends on the demand for the ___ (worker's output / input itself / substitute good).
Answers: 1. Marginal product; marginal revenue. 2. MRP; MRC. 3. Horizontal (perfectly elastic at the market wage). 4. Greater than. 5. = (equals). 6. Worker's output (the good being produced).

AP Microeconomics — Practice Problems: Unit 6

Section A: Externalities

1. A factory produces steel and emits pollution into a nearby river, harming fishermen downstream. This is an example of:

(A) A positive externality in production
(B) A negative externality in production
(C) A positive externality in consumption
(D) A negative externality in consumption
(E) A public good
Answer: B. The factory's production imposes costs on third parties (fishermen) who are not involved in the transaction. This is a negative externality in production. The social cost of production exceeds the private cost.

2. In a market with a negative production externality, the free market produces:
(A) Less than the socially optimal quantity
(B) More than the socially optimal quantity
(C) Exactly the socially optimal quantity
(D) Zero output
(E) Output where MSB = MSC
Answer: B. A negative externality means the firm ignores the external cost. It produces where private MC = private MB (demand). The socially optimal quantity is where social MC = social MB. Since social MC > private MC, the firm overproduces.

3. A per-unit tax on a good that generates a negative externality should be set equal to:
(A) The market price
(B) The marginal external cost
(C) The total external cost
(D) Consumer surplus
(E) Producer surplus
Answer: B. A Pigouvian tax equal to the marginal external cost internalizes the externality, shifting the private supply curve to equal the social supply curve. This corrects the overproduction and achieves the socially optimal output where MSC = MSB.

4. Vaccinations create a positive externality because when one person gets vaccinated, others benefit from reduced transmission. Without government intervention, the market will:
(A) Produce more than the socially optimal quantity
(B) Produce less than the socially optimal quantity
(C) Produce the socially optimal quantity
(D) Produce zero output
(E) Overprice vaccinations
Answer: B. Positive externalities mean the social benefit exceeds the private benefit. Consumers only consider their private benefit, so they demand too little. The market underproduces relative to the socially optimal level. A per-unit subsidy equal to the marginal external benefit can correct this.

Section B: Calculating with Externalities

5. The market for paper has the following information:

Private demand: MPB = 100 − Q (this also equals MSB since no consumption externality)
Private supply: MPC = 20 + Q
External cost per unit: $10
Calculate:
(a) The free market equilibrium (without government intervention)
(b) The socially optimal equilibrium
(c) The per-unit tax needed to correct the externality
(d) The deadweight loss without intervention
Solution:
(a) Free market: MPB = MPC → 100 − Q = 20 + Q → 80 = 2Q → Q = 40, P = $60
(b) Socially optimal: MSB = MSC. MSC = MPC + External cost = (20 + Q) + 10 = 30 + Q.
MSB = MSC → 100 − Q = 30 + Q → 70 = 2Q → Q = 35, P (demand price) = $65
(c) Per-unit tax = marginal external cost = $10
(d) DWL = ½ × external cost × (Qmarket − Qoptimal) = ½ × 10 × (40 − 35) = ½ × 10 × 5 = $25
6. Education generates a positive externality of $8 per student. If the private demand for college education is P = 50 − Q and the private supply is P = 10 + Q:
(a) Find the market equilibrium without intervention
(b) Find the socially optimal output
(c) What per-unit subsidy achieves the optimal outcome?
Solution:
(a) Market: 50 − Q = 10 + Q → 40 = 2Q → Q = 20, P = $30
(b) MSB = MPB + external benefit = (50 − Q) + 8 = 58 − Q
MSC = 10 + Q (no production externality) MSB = MSC → 58 − Q = 10 + Q → 48 = 2Q → Q = 24 Price on demand curve = 50 − 24 = $26; Price on supply curve = 10 + 24 = $34
(c) Per-unit subsidy = $8 (marginal external benefit). This shifts the demand curve up by $8, leading to the optimal quantity.

Section C: Public Goods and Common Resources

7. Classify each of the following as a public good, private good, common resource, or club good:

(a) A lighthouse
(b) A slice of pizza
(c) Fish in the ocean
(d) Cable television
Solution:
(a) Lighthouse: Public good (non-excludable and non-rivalrous)
(b) Slice of pizza: Private good (excludable and rivalrous)
(c) Fish in the ocean: Common resource (non-excludable but rivalrous)
(d) Cable television: Club good (excludable but non-rivalrous)
8. The tragedy of the commons occurs because:
(A) Private goods are overproduced
(B) Common resources are overused since no individual has an incentive to conserve
(C) Public goods are underproduced
(D) Governments regulate too much
(E) Firms collude to restrict output
Answer: B. When a resource is non-excludable but rivalrous, individuals can access it freely but their use depletes it for others. Since no one owns the resource, no one has an incentive to conserve it, leading to overuse and depletion (tragedy of the commons).

Section D: Income Distribution

9. If the Lorenz curve moves further away from the line of equality, this indicates:

(A) Greater income equality
(B) Greater income inequality
(C) No change in income distribution
(D) A decrease in the Gini coefficient
(E) Perfect income equality
Answer: B. The Lorenz curve plots cumulative income against cumulative households. The line of equality (45-degree line) represents perfect equality. As the Lorenz curve bows further away from this line, income distribution becomes more unequal.

10. The Gini coefficient ranges from:
(A) −1 to 1
(B) 0 to 1
(C) 0 to 100
(D) 1 to 10
(E) 0% to 100%
Answer: B. The Gini coefficient ranges from 0 (perfect equality) to 1 (maximum inequality). A higher Gini coefficient indicates greater income inequality. (Note: sometimes expressed as 0 to 100, but 0 to 1 is the standard economic convention.)

11. Government policies that can reduce income inequality include:
(A) Progressive taxation (higher tax rates for higher incomes)
(B) Transfer payments (welfare, Social Security, food stamps)
(C) Provision of public goods like education and healthcare
(D) Minimum wage laws
(E) All of the above
Answer: E. All of these policies are tools the government uses to redistribute income and reduce inequality. Progressive taxes take more from higher earners, transfer payments provide support to lower-income individuals, public goods provision improves access, and minimum wage laws set a floor on earnings.

Section E: Government Intervention Methods

12. Match each government intervention to the market failure it addresses:

Intervention	Market Failure
Per-unit Pigouvian tax	Negative externality
Per-unit subsidy	Positive externality
Direct provision by government	Public goods (underproduction)
Tradable permits (cap & trade)	Negative externality (pollution)
Assignment of property rights	Common resource (tragedy of commons)

Self-Check Quiz

A negative externality in production means MSC is ___ (greater than / less than / equal to) MPC.
A Pigouvian tax shifts the ___ (supply/demand) curve to internalize the externality.
A public good is both ___ and ___. (excludable/non-excludable; rivalrous/non-rivalrous)
The Coase Theorem states that private bargaining can resolve externalities if transaction costs are ___ and property rights are well-defined. (low / high)
A Gini coefficient of 0.50 indicates ___ (more / less) inequality than a coefficient of 0.25.
The free rider problem is associated with ___ goods. (public / private / common resource)
Answers: 1. Greater than. 2. Supply (for production externality). 3. Non-excludable; non-rivalrous. 4. Low. 5. More. 6. Public.

Summary & cheat sheets

AP Microeconomics — Comprehensive Summary Sheet

UNIT 1: Basic Economic Concepts (12–18%)

Scarcity & Opportunity Cost

Scarcity: Unlimited wants, limited resources → choices must be made
Opportunity cost: Value of next best alternative forgone
Production Possibilities Curve (PPC):
- Points ON curve = efficient, INSIDE = inefficient, OUTSIDE = unattainable
- Concave (bowed out) = increasing opportunity costs
- Shifts outward = economic growth (tech, resources, education)

Comparative & Absolute Advantage

Absolute advantage: Can produce MORE of a good with the same resources (lower resource cost)
Comparative advantage: Can produce at a LOWER OPPORTUNITY COST (the basis for trade)
Specialization & Trade: Countries should specialize in goods where they have comparative advantage → both gain from trade
To find comparative advantage: calculate opportunity cost for each country, compare

Demand & Supply

Law of Demand: Price ↑ → Quantity demanded ↓ (inverse relationship)
Law of Supply: Price ↑ → Quantity supplied ↑ (direct relationship)
Demand shifters: Income (normal vs. inferior), tastes, prices of related goods (substitutes/complements), expectations, number of buyers
Supply shifters: Input prices, technology, expectations, number of sellers, government policies

Market Equilibrium

Equilibrium: Qd = Qs (no surplus or shortage)
Surplus: P > Pe → Qs > Qd → price falls
Shortage: P < Pe → Qd > Qs → price rises

Price Controls

Price ceiling: Maximum legal price. Binding if set BELOW equilibrium → shortage
Price floor: Minimum legal price. Binding if set ABOVE equilibrium → surplus
Both create deadweight loss (reduced total surplus)

UNIT 2: Supply and Demand (20–25%)

Price Elasticity of Demand (Ed)

Value	Type	TR when P↑	TR when P↓
Ed > 1	Elastic	TR↓	TR↑
Ed = 1	Unit elastic	TR unchanged	TR unchanged
Ed < 1	Inelastic	TR↑	TR↓

Determinants of Elasticity:

Substitutes: More substitutes → more elastic
Proportion of income: Larger share → more elastic
Time: Longer time horizon → more elastic
Definition: Narrower market → more elastic

Midpoint Method:

Ed = |(Q2−Q1)/((Q2+Q1)/2)| ÷ |(P2−P1)/((P2+P1)/2)|

Cross-Price Elasticity

Ecross > 0: Substitutes (price of A↑ → demand for B↑)
Ecross < 0: Complements (price of A↑ → demand for B↓)
Ecross = 0: Unrelated goods

Income Elasticity

Eincome > 0: Normal good (E > 1 = luxury, 0 < E < 1 = necessity)
Eincome < 0: Inferior good

Consumer & Producer Surplus

Consumer surplus (CS): Area below demand, above price
Producer surplus (PS): Area above supply, below price
Total surplus = CS + PS (maximized at equilibrium)

Tax Incidence

Tax burden falls more on the less elastic side of the market
Deadweight loss (DWL): ½ × tax per unit × (Q before tax − Q after tax)
DWL is larger when demand/supply is more elastic

UNIT 3: Production, Costs, and Perfect Competition (22–28%)

Key Cost Formulas

Cost	Formula
Total Cost (TC)	TFC + TVC
Total Fixed Cost (TFC)	Constant at all output levels
Total Variable Cost (TVC)	Sum of all variable costs
Average Total Cost (ATC)	TC / Q = AFC + AVC
Average Fixed Cost (AFC)	TFC / Q (always decreasing)
Average Variable Cost (AVC)	TVC / Q
Marginal Cost (MC)	ΔTC / ΔQ

Key Relationships

MC intersects ATC and AVC at their minimum points
When MC < ATC → ATC is falling; when MC > ATC → ATC is rising
Law of diminishing marginal returns: MP eventually decreases → MC eventually increases

Long-Run Costs

Economies of scale: LRATC decreases as output increases
Constant returns to scale: LRATC stays the same
Diseconomies of scale: LRATC increases as output increases

Perfect Competition

Feature	Perfect Competition
Sellers	Many (price takers)
Product	Identical (homogeneous)
Entry/Exit	Free
Demand curve	Perfectly elastic (horizontal at P)
Profit max rule	MR = MC = P
Short run	Can earn profit, loss, or break even
Long run	P = min ATC = MC (zero economic profit)
Efficiency	Both allocative (P=MC) and productive (P=min ATC)

Shutdown Rule:

Short run: Shut down if P < AVC (loss = TFC vs. loss > TFC)
Long run: Exit if P < ATC (economic loss exists)

UNIT 4: Imperfect Competition (15–22%)

Comparison of Market Structures

Feature	Monopoly	Monopolistic Comp	Oligopoly
Sellers	One	Many	Few
Product	Unique	Differentiated	Standard or differentiated
Barriers	High	Low	High
Price power	Price maker	Some price power	Strategic interdependence
Demand curve	Market demand	Downward sloping	Kinked or game theory
Long-run profit	Positive	Zero	Can be positive
Efficiency	Neither	Neither	Neither

Monopoly

Profit max: MR = MC, charge P on demand curve
MR curve below demand (for linear: twice the slope)
P > MC → allocative inefficiency → deadweight loss
Barriers: Natural monopoly, patents, government licenses, ownership of resources
Price discrimination: Charge different prices to different groups
- Conditions: market power, identify groups, prevent resale
- Perfect (1st degree): charge each consumer max WTP → CS = 0, DWL = 0
- 3rd degree: different prices for different groups based on elasticity
Natural monopoly regulation: P = MC (efficient but firm loses $), P = ATC (fair return)

Monopolistic Competition

Short run: MR = MC, P > MC, can earn profit or loss
Long run: Zero economic profit (P = ATC), P > MC, excess capacity
Product differentiation through advertising, branding, quality

Oligopoly

Game theory: Models strategic interdependence
Prisoner's dilemma: Nash equilibrium ≠ best collective outcome
Dominant strategy: Best regardless of opponent's choice
Nash equilibrium: Each player's strategy is optimal given others' strategies
Cartel: Collusion to act as monopoly → inherently unstable (incentive to cheat)
Kinked demand: Rivals match price cuts but not increases → price rigidity

UNIT 5: Factor Markets (8–12%)

Key Concepts

MRP (Marginal Revenue Product): MP × MR = additional revenue from one more unit of labor
MRC (Marginal Resource Cost): Additional cost of one more unit of labor
Hiring rule: Hire where MRP = MRC (in competitive labor market: MRP = wage)

Perfectly Competitive Labor Market

Market determines wage (intersection of labor demand and supply)
Individual firm: wage taker, horizontal labor supply curve at market wage
Labor demand = downward-sloping MRP curve

Monopsony

Single buyer of labor
MRC > wage (must raise wage for all workers to hire one more)
Hires less labor and pays lower wage than competitive market
Deadweight loss in factor market

Cost Minimization

Least-cost rule: MPL/w = MPK/r (equal marginal product per dollar spent)
If MPL/w > MPK/r → use more labor, less capital
If MPL/w < MPK/r → use more capital, less labor

Shifts in Labor Demand

Increase in product price → MRP increases → labor demand shifts right
Technology improvement → MP increases → MRP increases → labor demand shifts right
Price of substitute input changes → substitution and scale effects

UNIT 6: Market Failure & Government (8–12%)

Externalities

Type	Problem	Solution
Negative production	MSC > MPC, overproduction	Per-unit tax = MEC
Negative consumption	MSB < MPB, overconsumption	Per-unit tax or regulation
Positive production	MSC < MPC, underproduction	Per-unit subsidy = MEB
Positive consumption	MSB > MPB, underconsumption	Per-unit subsidy

Social cost = Private cost + External cost
Social benefit = Private benefit + External benefit
Coase Theorem: If transaction costs are low and property rights well-defined, private bargaining can resolve externalities efficiently

Goods Classification

	Excludable	Non-excludable
Rivalrous	Private goods (pizza)	Common resources (fish in ocean)
Non-rivalrous	Club goods (cable TV)	Public goods (national defense)

Public goods: Underproduced by market due to free rider problem → government provision
Common resources: Overused (tragedy of the commons) → government regulation or property rights

Income Distribution

Lorenz curve: Plots cumulative income share vs. cumulative population share
Gini coefficient: Ratio of area between Lorenz curve and equality line to total area under equality line
- Range: 0 (perfect equality) to 1 (maximum inequality)
- Higher Gini = more inequality

Government Policies

Progressive taxation: Higher income → higher tax rate → reduces inequality
Transfer payments: Welfare, Social Security, unemployment benefits → redistributes income
Regulation: Environmental standards, minimum wage, antitrust laws

KEY FORMULAS — MASTER LIST

Concept	Formula
Price elasticity of demand	Ed = \	(%ΔQd)/(%ΔP)\	(midpoint method)
Total Revenue	TR = P × Q
Cross-price elasticity	Ecross = (%ΔQd of B)/(%ΔP of A)
Income elasticity	Eincome = (%ΔQd)/(%ΔIncome)
Accounting profit	Total revenue − explicit costs
Economic profit	Total revenue − (explicit + implicit costs)
Marginal product	MP = ΔTP / ΔL
Marginal cost	MC = ΔTC / ΔQ
Average total cost	ATC = TC/Q
MRP (labor)	MRP = MP × MR (in PC: MP × P)
Deadweight loss (tax)	DWL = ½ × tax × ΔQ
Deadweight loss (monopoly)	DWL = ½ × (Pm − Pae) × (Qae − Qm)
Gini coefficient	A/(A+B) where A = area between Lorenz and equality

Exam strategy

AP Microeconomics — Exam Strategy Guide

Exam Overview

Section	Questions	Time	Weight	Time per Question
Multiple Choice	60 questions	70 min	66.7%	~70 seconds
Free Response	3 questions	60 min	33.3%	~20 minutes
Total	63 questions	130 min	100%	—

MULTIPLE-CHOICE STRATEGIES

1. Time Management

70 seconds per question. That's tight. Don't get bogged down.
If you're unsure, mark it and move on. Come back at the end.
Skip hard questions initially. Answer easy ones first to secure points.
Pace yourself: Aim for 15 questions per 17–18 minutes. Check your pace at Q15, Q30, Q45.

2. Process of Elimination

Eliminate clearly wrong answers first. Even eliminating 2 options gives you a 33% chance of guessing correctly.
Look for distractors: Common wrong answers often include:
- Confusing "change in demand" (shift) with "change in quantity demanded" (movement along curve)
- Reversing the relationship (e.g., saying surplus instead of shortage)
- Using the wrong elasticity interpretation

3. Key Words to Watch

"Binding" price ceiling/floor: Means it actually affects the market
"Initially in equilibrium": Start your analysis from equilibrium
"Normal good" vs. "inferior good": Changes everything about income effects
"Short run" vs. "long run": Different rules for costs, profits, entry/exit
"Assume ceteris paribus": Only the stated factor changes

4. High-Frequency Question Types (Memorize These)

Topic	What They'll Ask
Elasticity	Is it elastic/inelastic? What happens to TR?
Tax incidence	Who bears the burden? (less elastic side)
Shutdown rule	P < AVC? Should the firm shut down?
Perfect competition long run	P = MC = min ATC, zero economic profit
Monopoly profit max	Set MR = MC, find P on demand curve
Externalities	Overproduction (negative) or underproduction (positive)
Comparative advantage	Calculate opportunity costs, find who should specialize

5. Common Mistakes to Avoid

❌ Confusing demand (the whole curve) with quantity demanded (a point on the curve)
❌ Forgetting that MC intersects ATC at its minimum
❌ Saying monopoly produces where P = MC (it produces where MR = MC and charges P > MC)
❌ Confusing accounting profit with economic profit (economic profit subtracts implicit costs too)
❌ Thinking perfectly competitive firms earn zero profit in the short run (they can earn positive profit, just not in the long run)
❌ Confusing elasticity of demand with slope (elasticity varies along a linear demand curve; slope doesn't)

FREE-RESPONSE STRATEGIES

1. FRQ Structure

FRQ 1: Long FRQ (typically 5–7 parts, worth 50% of FRQ score)
FRQ 2: Medium FRQ (4–5 parts, worth ~33% of FRQ score)
FRQ 3: Short FRQ (3–4 parts, worth ~17% of FRQ score)
Time allocation: FRQ1: ~25 min, FRQ2: ~20 min, FRQ3: ~15 min

2. Graphing is Essential

Every FRQ will require at least one graph. Practice graphing quickly and accurately.
Must-haves on every graph:
- Labeled axes (Price and Quantity)
- Labeled curves (D, S, MR, MC, ATC, etc.)
- Key points marked (Pe, Qe, Pm, Qm, etc.)
- Shifts clearly shown with arrows
- Shaded areas clearly labeled (DWL, tax revenue, CS, PS)

Graph Checklist:

[ ] Axes labeled? (P and Q — NOT x and y)
[ ] All curves labeled?
[ ] Equilibrium points marked?
[ ] Shifts shown correctly? (supply shifts UP = shifts LEFT)
[ ] Shaded areas labeled?
[ ] Arrows showing direction of change?

3. Written Responses

Use economic vocabulary. "Consumer surplus decreases" not "people pay more."
Explain, don't just state. If asked "why," give a reason:
- Bad: "CS decreases."
- Good: "CS decreases because the price ceiling creates a shortage, reducing the quantity traded below the equilibrium level."
Show your math. Even if you make a calculation error, showing your work can earn partial credit.
"Because" is your best friend. Every explanation should include a reason.

4. FRQ Point Distribution

Points are typically allocated as follows:

Graphing: 1–3 points per graph
Identification: 1 point per correct label, shift, or equilibrium
Explanation: 1 point per clear, correct economic reasoning
Calculation: 1 point per correct numerical answer (partial credit if work shown)

5. Specific FRQ Strategies by Unit

Demand & Supply Questions:

Always start from equilibrium
Shift the correct curve (demand shifters ≠ supply shifters)
Show new equilibrium clearly
Explain the transition process

Cost/Perfect Competition Questions:

Know your cost curves: TC, ATC, AVC, AFC, MC
Shutdown rule: compare P to AVC, not P to ATC
Long run: explain entry/exit process

Monopoly Questions:

Always find MR = MC first, then go UP to demand to find P
Remember: P > MC for monopoly (allocative inefficiency)
DWL triangle between MC and demand, from Qm to Qae

Factor Market Questions:

MRP = MP × MR (or MP × P in perfect competition)
Hire where MRP = MRC (or wage in competitive market)
Monopsony: MRC > wage, hire less, pay less

Externality Questions:

Negative externality: MSC > MPC, draw BOTH curves
Show overproduction and DWL
Tax = marginal external cost → supply shifts to MSC

STUDY PLAN (Final 4 Weeks)

Week 1: Foundations

Review Units 1 and 2 (40% of exam combined)
Focus on: PPC, opportunity cost, supply/demand shifts, equilibrium, elasticity
Practice: Complete 02-practice-unit1.md and 02-practice-unit2.md
Daily: 15 MCQ from Units 1–2

Week 2: Core Models

Review Units 3 and 4 (37–50% of exam combined)
Focus on: Cost curves, perfect competition, monopoly, game theory
Practice: Complete 02-practice-unit3.md and 02-practice-unit4.md
Daily: Graph at least one market structure perfectly

Week 3: Factor Markets & Government

Review Units 5 and 6 (16–24% of exam combined)
Focus on: MRP/MRC, monopsony, externalities, public goods
Practice: Complete 02-practice-unit5.md and 02-practice-unit6.md
Daily: 10 MCQ from Units 5–6 + review

Week 4: Full Preparation

Take full practice exam under timed conditions
Review all mistakes thoroughly
Re-read 04-summary-sheet.md daily
Practice FRQ graphing (draw graphs from memory)
Day before exam: Light review of summary sheet and formulas only

DAY-OF-EXAM TIPS

Before the Exam

Sleep well the night before (at least 7 hours)
Eat a balanced meal — your brain needs fuel
Arrive early — rushing increases anxiety
Bring: No. 2 pencils, pens (blue/black), photo ID
NO calculator needed — AP Micro does not allow calculators

During the Exam

Breathe. Take 30 seconds before starting to calm your nerves.
MCQ: Read the question stem FIRST, then the answers. Don't read answers first — they can bias your thinking.
MCQ: If you eliminate 2+ answers, guess immediately. Don't waste time.
MCQ: Answer every question. There is NO penalty for wrong answers.
FRQ: Read the ENTIRE FRQ before starting to write. Plan your answer.
FRQ: Graph BIG and CLEAR. Small graphs get lost and lose points.
FRQ: Use PEN for FRQ (required). Use pencil only for graphs.
Time check: At 60 min into MCQ, you should be at Q50 or beyond.

Mental Strategy

Don't panic on hard questions. Some questions are designed to be difficult. Your competition is struggling too.
Skip and return. Don't let one question derail your pacing.
Trust your preparation. If you've studied consistently, the answers are in your brain.
Stay until the end. Every point matters. Use every minute.

QUICK REFERENCE: What to Memorize Cold

Shutdown rule: P < AVC → shut down
Profit max (all firms): MR = MC
Perfect competition long run: P = MC = min ATC, π = 0
Monopoly: MR = MC, P on demand curve, P > MC, DWL exists
Elasticity rules: Ed > 1 → P↑ TR↓; Ed < 1 → P↑ TR↑
Tax incidence: Less elastic side bears more burden
Externalities: Negative → tax; Positive → subsidy; both = MEC or MEB
Hiring rule: MRP = MRC (competitive labor: MRP = wage)
Cost minimization: MPL/w = MPK/r
Deadweight loss formula: ½ × tax × ΔQ
Memorize these 10 items and you'll have the foundation for the vast majority of AP Micro questions. Everything else builds from these core principles.

Presentation outline

AP Microeconomics — Presentation Outline

Target Audience: AP Microeconomics students preparing for the exam Duration: 90–120 minutes (adjustable) Format: Slides with speaker notes, graphs, and practice questions

PART 1: INTRODUCTION (5 minutes)

Slide 1: Title Slide

AP Microeconomics Exam Review
6 Units, 130 Minutes, 1 Goal: MAXIMIZE YOUR SCORE
Presenter name and date

Slide 2: Exam Format Overview

60 MCQ in 70 min (66.7% of score)
3 FRQ in 60 min (33.3% of score)
No calculator allowed
Unit weighting pie chart:
- Unit 1: 12–18%
- Unit 2: 20–25%
- Unit 3: 22–28%
- Unit 4: 15–22%
- Unit 5: 8–12%
- Unit 6: 8–12%
  Speaker note: Emphasize that Units 2 and 3 together make up 42–53% of the exam. These are the highest-yield areas to study.

PART 2: UNIT 1 — Basic Economic Concepts (10 minutes)

Slide 3: Scarcity & the PPC

Definition of scarcity
PPC diagram: efficient, inefficient, unattainable points
PPC shifts outward: economic growth (tech, resources, education)
Increasing opportunity costs (concave shape)

Slide 4: Comparative Advantage

Absolute advantage vs. comparative advantage
Rule: Calculate opportunity cost for each country
Specialize in the good with LOWER opportunity cost
Example: Country A (10 cars or 5 trucks) vs. Country B (6 cars or 3 trucks)
- A's opportunity cost of 1 car = 0.5 trucks; B's = 0.5 trucks
- Same opportunity costs → no comparative advantage → no gains from trade

Slide 5: Supply and Demand Basics

Law of Demand: P↑ → Qd↓ (inverse)
Law of Supply: P↑ → Qs↑ (direct)
Shifters of demand: income, tastes, prices of related goods, expectations, number of buyers
Shifters of supply: input prices, technology, expectations, number of sellers, government policies
Key distinction: "Change in demand" (shift) vs. "change in quantity demanded" (movement)

Slide 6: Equilibrium, Surplus, and Shortage

Equilibrium graph: D and S intersect at Pe, Qe
Price ceiling below Pe → shortage
Price floor above Pe → surplus
Deadweight loss from price controls
Speaker note: Draw each graph live if possible. Emphasize that price ceilings create SHORTAGES (not surpluses) and price floors create SURPLUSES (not shortages). This is a very common exam trap.

PART 3: UNIT 2 — Supply and Demand Deep Dive (15 minutes)

Slide 7: Price Elasticity of Demand

Definition: responsiveness of Qd to price change
Midpoint method formula: Ed = |(%ΔQd)/(%ΔP)|
Categories: elastic (>1), unit (=1), inelastic (<1), perfectly elastic (∞), perfectly inelastic (0)

Slide 8: Elasticity and Total Revenue

Visual: Table showing Ed vs. TR when P↑ vs. P↓
Inelastic: P and TR move SAME direction
Elastic: P and TR move OPPOSITE direction
Determinants: substitutes, proportion of income, time, market definition

Slide 9: Cross-Price and Income Elasticity

Cross-price: substitutes (+), complements (−)
Income: normal (+), inferior (−), luxury (>1), necessity (0–1)
Quick practice: "Ramen noodles income elasticity?" → negative (inferior)

Slide 10: Consumer and Producer Surplus

Graph: Equilibrium with CS (below D, above P) and PS (above S, below P) shaded
Total surplus = CS + PS (maximized at equilibrium)
Deadweight loss: surplus lost due to market distortion

Slide 11: Tax Incidence and Deadweight Loss

Tax on sellers graph: supply shifts left by tax amount
Buyers pay more, sellers receive less
KEY RULE: Less elastic side bears MORE tax burden
DWL = ½ × tax × ΔQ
DWL larger with more elastic curves
Speaker note: Walk through a numeric example. Market with demand P=100-Q, supply P=20+Q, $4 tax. Show: Q drops from 40 to 38, buyers pay $62, sellers keep $58, DWL = $4.

PART 4: UNIT 3 — Production, Costs, and Perfect Competition (20 minutes)

Slide 12: Production Functions

Total product, marginal product, average product
Graph of MP: initially rises (increasing returns), then falls (diminishing returns), eventually negative
Law of diminishing marginal returns: MP eventually decreases

Slide 13: Short-Run Cost Curves

MASTER GRAPH showing AFC, AVC, ATC, MC
Key relationships:
- AFC always decreasing (asymptotic to zero)
- MC intersects AVC and ATC at their MINIMUMS
- ATC = AFC + AVC
Shutdown point: P = min AVC
Breakeven point: P = min ATC

Slide 14: Long-Run Costs

LRATC curve (envelope of short-run ATC curves)
Economies of scale: LRATC↓ as Q↑
Constant returns: LRATC flat
Diseconomies of scale: LRATC↑ as Q↑
Minimum efficient scale

Slide 15: Perfect Competition

Characteristics: many firms, identical products, price taker, free entry/exit
Firm's demand = MR = P (perfectly elastic)
Profit max: produce where P = MC
Short-run outcomes: profit, loss, or break even
Shut down if P < AVC

Slide 16: Perfect Competition Long-Run Equilibrium

Graph: P = MC = minimum ATC
Zero economic profit (normal profit)
Process: Positive profits attract entry → supply shifts right → price falls → profits eliminated
Both allocative efficiency (P=MC) and productive efficiency (P=min ATC)
Speaker note: Spend extra time here. This is the highest-weighted unit on the exam. Do a live example: TC = 100 + 10Q + Q², P = $20. Find MC, set = P, get Q = 5, calculate profit = −$75, check shutdown (AVC = $15 < P = $20, so produce in SR but exit in LR).

PART 5: UNIT 4 — Imperfect Competition (15 minutes)

Slide 17: Monopoly

Characteristics: single seller, unique product, high barriers to entry, price maker
Profit max: MR = MC, price on demand curve
P > MC → allocative inefficiency → deadweight loss
Sources of barriers: natural monopoly, patents, government licenses, resource ownership

Slide 18: Monopoly Graph

Master graph: D, MR (steeper than D), MC, ATC
Mark Qm (where MR=MC), Pm (on D above Qm)
Mark Qae (where D=MC), Pae (on D above Qae)
Shade DWL between Qm and Qae
Economic profit rectangle (if Pm > ATC at Qm)

Slide 19: Price Discrimination

Conditions: market power, identifiable groups, prevent resale
Perfect (1st degree): charge each consumer max WTP → CS = 0, DWL = 0
3rd degree: different prices for different groups
Higher price for less elastic group

Slide 20: Monopolistic Competition

Many firms, differentiated products, free entry/exit
Short run: MR = MC, can earn profit or loss (like monopoly)
Long run: P = ATC (zero profit), but P > MC and P > min ATC
Excess capacity: produces less than efficient scale
Advertising and product differentiation

Slide 21: Oligopoly and Game Theory

Few firms, interdependent decisions
Prisoner's dilemma payoff matrix
Dominant strategy and Nash equilibrium
Cartels: act as monopoly → inherently unstable (cheating incentive)
Kinked demand curve: price rigidity
Speaker note: Do a live prisoner's dilemma example. Show that both firms advertising is the Nash equilibrium but both would be better off not advertising. This is guaranteed to appear on the exam.

PART 6: UNIT 5 — Factor Markets (10 minutes)

Slide 22: Derived Demand and MRP

Labor demand is DERIVED from product demand
MRP = MP × MR (in PC: MRP = MP × P)
MRP curve = labor demand curve (downward sloping due to diminishing MP)
Hiring rule: hire until MRP = MRC (wage in competitive market)

Slide 23: Competitive vs. Monopsony Labor Markets

Competitive: Many employers, wage = MRC, horizontal supply curve at market wage
Monopsony: Single employer, MRC > wage, hires less and pays less
Graph comparison side by side
Deadweight loss from monopsony

Slide 24: Cost-Minimizing Resource Combination

Rule: MPL/w = MPK/r
If MPL/w > MPK/r → hire more labor (more output per dollar)
If MPL/w < MPK/r → hire more capital
Adjustment continues until ratios are equal

PART 7: UNIT 6 — Market Failure and Government (10 minutes)

Slide 25: Externalities

Negative production externality: MSC > MPC → overproduction → DWL
Positive consumption externality: MSB > MPB → underconsumption → DWL
Solutions:
- Negative: per-unit Pigouvian tax = marginal external cost
- Positive: per-unit subsidy = marginal external benefit
Graph showing MSC, MPC, MSB, MPB, market quantity, socially optimal quantity, DWL

Slide 26: Public Goods and Common Resources

2×2 classification matrix:
- Private goods: excludable + rivalrous
- Public goods: non-excludable + non-rivalrous (national defense)
- Common resources: non-excludable + rivalrous (fish, grazing land)
- Club goods: excludable + non-rivalrous (cable TV)
Free rider problem → public goods underproduced
Tragedy of the commons → common resources overused

Slide 27: Income Distribution

Lorenz curve: cumulative income vs. cumulative population
Gini coefficient: 0 (equality) to 1 (max inequality)
Government tools: progressive taxes, transfer payments, public services
Trade-off: redistribution vs. efficiency

PART 8: EXAM STRATEGY AND WRAP-UP (10 minutes)

Slide 28: Top 10 Things to Memorize

Shutdown rule: P < AVC → shut down
Profit max: MR = MC (all market structures)
PC long run: P = MC = min ATC
Monopoly: MR = MC, P on D, P > MC
Elasticity: Ed > 1 → P↑ = TR↓
Tax incidence: less elastic side pays more
Externalities: negative → tax, positive → subsidy
Hiring: MRP = MRC
Cost min: MPL/w = MPK/r
DWL = ½ × tax × ΔQ

Slide 29: MCQ Strategy

70 seconds per question
Process of elimination
Answer every question (no penalty for guessing)
Skip hard ones, return later
Watch for traps: shift vs. movement, short run vs. long run

Slide 30: FRQ Strategy

Always label axes (P and Q)
Always label all curves
Shade and label areas (DWL, tax revenue, CS, PS)
Explain with "because"
Show math work for partial credit
Use economic vocabulary

Slide 31: Study Plan

Week 1: Units 1–2 (foundations)
Week 2: Units 3–4 (core models)
Week 3: Units 5–6 (applications)
Week 4: Full practice exam, review mistakes

Slide 32: Final Encouragement

You've got this!
Trust your preparation
Every point matters
Good luck on the AP Micro exam!
Speaker note: End with a 5-minute Q&A session. Have students ask about any confusing topics. If time permits, do a rapid-fire round of key concept questions.

Audio script

AP Microeconomics — Audio Review Script

Estimated Runtime: 45–55 minutes at natural speaking pace

INTRODUCTION (2 minutes)

Welcome to the AP Microeconomics Audio Review. This script covers every unit tested on the AP Micro exam — all six units, the key concepts, formulas, and common pitfalls you need to know. Whether you're listening on your commute, during a workout, or as a final review the night before the exam, this guide has you covered.

The AP Micro exam has 60 multiple-choice questions worth 66.7% of your score, and 3 free-response questions worth 33.3%. You'll have 70 minutes for the MCQ section and 60 minutes for the FRQ section. No calculator is allowed.

Let's get started.

UNIT 1: BASIC ECONOMIC CONCEPTS (6 minutes)

Scarcity and Opportunity Cost

The entire field of economics exists because of one fundamental problem: scarcity. Human wants are unlimited, but resources — land, labor, capital, and entrepreneurship — are limited. This forces every society, and every individual, to make choices.

Every choice has an opportunity cost — the value of the next best alternative that you give up. If you spend three hours studying economics, the opportunity cost isn't "nothing" — it's whatever else you would have done with those three hours.

The Production Possibilities Curve

The PPC is a graph that shows all possible combinations of two goods an economy can produce, given its resources. Points ON the curve represent efficient production. Points INSIDE the curve mean resources are being underutilized — unemployment or inefficiency. Points OUTSIDE the curve are unattainable with current resources.

The PPC is typically bowed outward, or concave. This shape reflects the law of increasing opportunity costs: as you produce more of one good, you give up increasingly larger amounts of the other good.

The PPC shifts outward when there is economic growth — more resources, better technology, or an improved workforce.

Comparative and Absolute Advantage

This is a major exam topic. Listen carefully.

Absolute advantage means you can produce MORE of a good using the same resources. But comparative advantage — which is what matters for trade — means you can produce a good at a LOWER OPPORTUNITY COST.

To find comparative advantage, calculate the opportunity cost for each country for each good. The country with the lower opportunity cost for a particular good should specialize in that good.

Both countries gain from trade when they specialize according to comparative advantage, even if one country has an absolute advantage in everything. That's the magic of comparative advantage.

Demand, Supply, and Equilibrium

The law of demand says that as price goes up, quantity demanded goes down — an inverse relationship. The law of supply says that as price goes up, quantity supplied goes up — a direct relationship.

Market equilibrium occurs at the price where quantity demanded equals quantity supplied. At this price, there is no surplus and no shortage. The market clears.

A price ceiling set BELOW the equilibrium price creates a shortage — more people want to buy than sellers want to sell. A price floor set ABOVE the equilibrium price creates a surplus — sellers want to sell more than buyers want to buy.

Critical exam tip: Do NOT confuse a "change in demand" — which is a SHIFT of the entire demand curve — with a "change in quantity demanded" — which is a MOVEMENT ALONG the demand curve caused by a price change. This is tested on virtually every AP Micro exam.

UNIT 2: SUPPLY AND DEMAND (8 minutes)

Price Elasticity of Demand

Elasticity measures how responsive quantity demanded is to a price change. The formula using the midpoint method is: the absolute value of the percentage change in quantity demanded divided by the percentage change in price.

If elasticity is greater than 1, demand is elastic — consumers are responsive to price changes. If elasticity is less than 1, demand is inelastic — consumers are not very responsive. If it equals exactly 1, demand is unit elastic.

Here's the critical relationship with total revenue: If demand is inelastic and you raise the price, total revenue increases. If demand is elastic and you raise the price, total revenue decreases. This is a guaranteed exam question.

What determines elasticity? Four factors: (1) Availability of close substitutes — more substitutes means more elastic. (2) Proportion of income spent on the good — a larger share means more elastic. (3) Time horizon — longer time means more elastic as consumers adjust. (4) How narrowly the good is defined — "food" is inelastic, "Fuji apples" is elastic.

Cross-Price and Income Elasticity

Cross-price elasticity measures how the quantity demanded of one good responds to the price of another. If the value is positive, the goods are substitutes — like tea and coffee. If negative, they're complements — like hot dogs and hot dog buns.

Income elasticity measures how quantity demanded responds to income changes. For normal goods, income elasticity is positive. For inferior goods — things like ramen noodles or used clothing — income elasticity is negative. Luxury normal goods have an income elasticity greater than 1.

Consumer and Producer Surplus

Consumer surplus is the difference between what consumers are willing to pay and what they actually pay. On a graph, it's the area below the demand curve and above the market price.

Producer surplus is the difference between the price producers receive and their minimum acceptable price. It's the area above the supply curve and below the market price.

Total surplus — consumer surplus plus producer surplus — is maximized at market equilibrium. Any deviation from equilibrium, like a tax or price control, reduces total surplus.

Tax Incidence and Deadweight Loss

When a tax is imposed, the burden is shared between buyers and sellers. Here's the key rule: the side of the market that is LESS ELASTIC bears MORE of the tax burden.

Deadweight loss is the loss of total surplus that occurs because a tax (or price control) prevents some mutually beneficial transactions. The formula is: one-half times the tax per unit times the reduction in quantity.

Deadweight loss is larger when supply and demand are elastic, because elastic curves mean the tax causes a bigger reduction in quantity traded.

UNIT 3: PRODUCTION, COSTS, AND PERFECT COMPETITION (12 minutes)

This is the most heavily weighted unit on the exam. Pay close attention.

Production Functions

In the short run, at least one input is fixed. When a firm adds more of a variable input — like labor — to a fixed input — like capital — the marginal product initially increases due to increasing marginal returns, then eventually decreases due to the law of diminishing marginal returns.

When marginal product decreases, marginal cost increases. That's the key connection.

Short-Run Cost Curves

There are several cost curves you must know:

Total cost equals total fixed cost plus total variable cost. Average total cost equals TC divided by Q — or equivalently, average fixed cost plus average variable cost. Marginal cost equals the change in total cost divided by the change in quantity.

The critical relationship: Marginal cost intersects both AVC and ATC at their minimum points. When MC is below ATC, ATC is falling. When MC is above ATC, ATC is rising. They cross exactly at the bottom of the U-shaped ATC curve.

Average fixed cost always declines as output increases because you're spreading the same fixed cost over more units.

The shutdown point is where price equals minimum AVC. Below this price, the firm can't cover its variable costs and should shut down, losing only its fixed costs. The breakeven point is where price equals minimum ATC.

Perfect Competition

In a perfectly competitive market, there are many buyers and sellers, products are identical, firms are price takers, and there are no barriers to entry or exit.

Each firm faces a perfectly elastic — horizontal — demand curve at the market price. For a competitive firm, price equals marginal revenue.

The profit-maximizing rule for ALL firms is: produce where marginal revenue equals marginal cost. For a perfectly competitive firm, this simplifies to: produce where P equals MC.

In the short run, a competitive firm can earn positive profit, incur a loss, or break even. If P is greater than ATC at the profit-maximizing output, the firm earns positive economic profit. If P is between ATC and AVC, the firm has a loss but continues producing because it covers variable costs and some fixed costs. If P is less than AVC, the firm shuts down.

In the long run, free entry and entry drive economic profit to zero. When existing firms earn positive profit, new firms enter, supply shifts right, price falls, and profits are eliminated. The long-run equilibrium has price equal to MC and price equal to minimum ATC.

This means perfect competition achieves BOTH allocative efficiency — where P equals MC, producing the socially optimal quantity — AND productive efficiency — where goods are produced at the lowest possible per-unit cost.

Long-Run Costs and Economies of Scale

When a firm changes its plant size, its long-run average total cost may decrease — economies of scale — stay the same — constant returns to scale — or increase — diseconomies of scale.

Economies of scale occur because larger firms can specialize labor, buy inputs in bulk, and use more efficient technology. Diseconomies of scale occur because larger organizations become harder to manage and coordinate.

UNIT 4: IMPERFECT COMPETITION (10 minutes)

Monopoly

A monopoly is a single seller protected by barriers to entry. These barriers might be legal — like patents and government licenses — or natural — where one firm can supply the entire market at lower cost than multiple firms due to economies of scale.

The monopolist faces the entire downward-sloping market demand curve. To maximize profit, the monopolist produces where MR equals MC, just like any firm. But unlike a competitive firm, the monopolist then charges a price found on the demand curve ABOVE the MR = MC point.

This means the monopolist charges a price above marginal cost — P is greater than MC. This creates allocative inefficiency. The monopolist produces less than the socially optimal quantity, and the difference creates a deadweight loss.

The monopolist's marginal revenue curve lies below the demand curve. For a linear demand curve, MR has exactly twice the slope of demand. This is because to sell one more unit, the monopolist must lower the price on ALL units, not just the additional unit.

Price Discrimination

A monopolist can practice price discrimination — charging different prices to different consumers — if three conditions hold: the firm has market power, it can identify groups with different price sensitivities, and it can prevent resale between groups.

Under perfect, or first-degree, price discrimination, the monopolist charges each consumer their maximum willingness to pay. This eliminates all consumer surplus and, interestingly, eliminates deadweight loss — the monopolist produces the competitive output quantity because it captures all surplus.

Monopolistic Competition

Monopolistic competition has many firms selling differentiated products — think restaurants, clothing brands, or coffee shops. There is free entry and exit.

In the short run, each firm acts like a mini-monopoly: it faces a downward-sloping demand curve, produces where MR equals MC, and can earn positive profit or a loss.

In the long run, free entry eliminates economic profit. New firms enter when they see profits, increasing competition and reducing demand for each individual firm until P equals ATC. But here's the key difference from perfect competition: P does NOT equal minimum ATC. The monopolistically competitive firm produces at an output level below the minimum ATC point — this is called "excess capacity." The firm is NOT productively efficient, and P is greater than MC, so it's NOT allocatively efficient either.

Oligopoly

An oligopoly is a market with a few large firms whose decisions are interdependent — each firm's profit depends on what its rivals do.

Game theory models this strategic behavior. The prisoner's dilemma is the classic example: two firms each have a dominant strategy to cheat on a cartel agreement, but both would be better off cooperating. The Nash equilibrium — where each player's strategy is optimal given the other's — is not the best collective outcome.

In a cartel, firms collude to act as a monopoly, restricting output and raising prices. Cartels are inherently unstable because each member has an incentive to secretly produce more than its quota.

The kinked demand curve model assumes that rivals match price decreases but not price increases. This creates a gap in the marginal revenue curve at the current price, leading to price rigidity — prices tend to stay the same even when costs change.

UNIT 5: FACTOR MARKETS (5 minutes)

Derived Demand

The demand for labor is a DERIVED demand — it comes from the demand for the product that labor produces. If demand for the product increases, demand for labor increases too.

Marginal Revenue Product

The key concept: Marginal Revenue Product equals Marginal Product times Marginal Revenue. For a firm in a perfectly competitive product market, MRP equals MP times price.

MRP is the demand curve for labor — it's downward sloping because of diminishing marginal returns. Each additional worker adds less and less output.

Hiring Decision

The firm hires workers up to the point where MRP equals MRC — marginal resource cost. In a perfectly competitive labor market, MRC simply equals the market wage.

If the 5th worker's MRP is $80 and the wage is $50, hire the worker — they bring in more than they cost. If the 6th worker's MRP is $40, don't hire — they cost more than they produce.

Monopsony

A monopsony is a single buyer of labor — like a mining company in a small town. The monopsonist faces the upward-sloping market labor supply curve. To hire more workers, it must raise the wage for ALL workers, not just the new one. This means marginal resource cost exceeds the wage.

The monopsonist hires fewer workers and pays a lower wage than a competitive market would. This creates a deadweight loss in the factor market.

Cost Minimization

A firm minimizes its production costs when the marginal product per dollar spent is equal across all inputs: MPL divided by the wage equals MPK divided by the rental rate of capital. If labor gives more output per dollar than capital, the firm should hire more labor and less capital until the ratios equalize.

UNIT 6: MARKET FAILURE AND THE ROLE OF GOVERNMENT (7 minutes)

Externalities

An externality is a cost or benefit that affects a third party not involved in a transaction.

A negative production externality — like pollution from a factory — means the social cost of production exceeds the private cost. The market overproduces because the firm doesn't account for the external cost.

The solution: a Pigouvian tax equal to the marginal external cost. This shifts the supply curve up to reflect the full social cost, and the market produces the socially optimal quantity.

A positive externality — like education or vaccinations — means the social benefit exceeds the private benefit. The market underproduces. The solution is a per-unit subsidy equal to the marginal external benefit, shifting demand up to reflect the full social benefit.

Public Goods and Common Resources

Goods are classified by two characteristics: excludability and rivalrousness.

A public good — like national defense — is both non-excludable and non-rivalrous. Because people can benefit without paying (the free rider problem), private markets underproduce or fail to produce public goods entirely. Government provision is necessary.

Common resources — like fish in the ocean or public grazing land — are non-excludable but rivalrous. Since no one owns the resource, individuals overuse it for personal gain, leading to depletion. This is the tragedy of the commons. Solutions include government regulation, assignment of property rights, or tradable permits.

Income Distribution

The Lorenz curve plots the cumulative share of income received by cumulative percentages of households. The further the curve bows from the line of perfect equality, the more unequal the income distribution.

The Gini coefficient measures this inequality on a scale from 0 — perfect equality — to 1 — maximum inequality. A higher Gini means more inequality.

Government tools for reducing inequality include progressive taxation — higher tax rates on higher incomes — transfer payments like welfare and Social Security — and provision of public goods like education and healthcare.

EXAM STRATEGY AND FINAL TIPS (5 minutes)

Here are the top 10 things you must have memorized cold for the AP Micro exam:

Number one: The shutdown rule. A firm shuts down in the short run if price is less than average variable cost.

Number two: Profit maximization. ALL firms produce where marginal revenue equals marginal cost.

Number three: Perfect competition long run. Price equals MC equals minimum ATC, and economic profit is zero.

Number four: Monopoly pricing. Produce where MR equals MC, but charge the price found on the demand curve above that point. Price is always greater than MC.

Number five: Elasticity and total revenue. If demand is inelastic, raising price increases total revenue. If elastic, raising price decreases total revenue.

Number six: Tax incidence. The less elastic side of the market bears more of the tax burden.

Number seven: Externalities. Negative externalities are corrected with a per-unit tax. Positive externalities are corrected with a per-unit subsidy.

Number eight: Factor markets. Hire workers until marginal revenue product equals marginal resource cost — or the wage in a competitive labor market.

Number nine: Cost minimization. The ratio of marginal product to input price must be equal across all inputs.

Number ten: Deadweight loss. For a tax, DWL equals one-half times the tax per unit times the change in quantity.

For the multiple-choice section, pace yourself at about 70 seconds per question. Skip hard ones and come back. Answer every question — there is no penalty for guessing. Use process of elimination aggressively.

For the free-response section, label every axis with Price and Quantity. Label every curve. Shade and label areas like deadweight loss and tax revenue. Always explain your reasoning with the word "because." And show all math work — partial credit is your friend.

One last reminder: always distinguish between "change in demand" — a shift of the whole curve — and "change in quantity demanded" — a movement along the curve. This single distinction is responsible for more lost points than almost any other concept on the exam.

You've put in the work. Trust your preparation. Stay calm, stay focused, and go earn that 5.

Good luck on the AP Microeconomics exam!