Unit 3 Test: Production, Cost, and Perfect Competition
Practice AP Microeconomics Unit 3 with tests on cost curves, diminishing marginal returns, profit maximization, shutdown rules, and perfect competition equilibrium.
Understanding Firm Behavior in Perfectly Competitive Markets
Unit 3 shifts the focus from market-level supply and demand to the individual firm. AP Microeconomics expects students to draw, read, and analyze cost curve diagrams with precision. This unit is heavily tested in both the multiple-choice and free-response sections, particularly the long FRQ.
Key Topics in Unit 3
Diminishing Marginal Returns
As more units of a variable input (typically labor) are added to a fixed input (capital), marginal product eventually declines. This relationship directly determines the shape of cost curves. When marginal product is rising, marginal cost falls. When marginal product is falling, marginal cost rises. AP questions use this relationship to connect production theory to cost analysis.
Cost Curves: The Full Framework
The AP exam expects students to draw and interpret the following cost curves:
- Total Cost (TC) and its components: fixed cost (TFC) and variable cost (TVC).
- Marginal Cost (MC): the cost of producing one additional unit. U-shaped, intersects ATC and AVC at their minimum points.
- Average Total Cost (ATC): TC divided by quantity. U-shaped.
- Average Variable Cost (AVC): TVC divided by quantity. U-shaped, lies below ATC.
- Average Fixed Cost (AFC): TFC divided by quantity. Continuously declining.
Profit Maximization: P = MC Rule
A perfectly competitive firm is a price taker — it accepts the market price as given and chooses output to maximize profit. Profit is maximized where price equals marginal cost (P = MC), as long as price is above average variable cost. AP FRQs ask students to identify this output level on a graph and calculate profit or loss using the area between price and ATC.
Shutdown and Break-Even Rules
A firm shuts down in the short run when price falls below minimum AVC — the firm cannot cover variable costs. A firm breaks even when price equals minimum ATC — economic profit is zero. If price is between minimum AVC and minimum ATC, the firm operates at a loss but continues producing because it covers variable costs and contributes to fixed costs.
Short-Run and Long-Run Equilibrium
In the short run, perfectly competitive firms can earn economic profit or incur losses. In the long run, free entry and exit drive economic profit to zero. AP FRQs routinely ask students to draw the short-run situation (profit or loss) and then show the long-run adjustment, including whether new firms enter or existing firms exit and what happens to the market supply curve and equilibrium price.
AP FRQ Graph Skills for Unit 3
- Draw a correctly labeled cost curve diagram showing MC, ATC, and AVC with a given market price line (MR = P for a competitive firm).
- Identify the profit-maximizing output at the intersection of P and MC.
- Shade the profit region (when P is above ATC) or loss region (when P is below ATC).
- Show the long-run adjustment from a short-run profit or loss scenario.