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Unit 3: Production, Cost, and the Perfect Competition Model

7 dot points across 7 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

When should a firm keep producing at a loss, when should it shut down, and when does it enter or exit?

Topic 3.6 Firms' Short-Run Decisions to Produce and Long-Run Decisions to Enter or Exit: apply the shut-down rule using average variable cost, and the entry and exit conditions using average total cost and economic profit.
A focused answer to AP Microeconomics Topic 3.6, covering the short-run shut-down rule based on price versus average variable cost, the break-even point, and the long-run entry and exit decisions driven by economic profit, with worked exam-style questions.
10 min answer →

When all inputs can vary, how does long-run average cost behave, and what are economies and diseconomies of scale?

Topic 3.3 Long-Run Production Costs: explain the long-run average total cost curve as an envelope of short-run curves, and identify economies of scale, diseconomies of scale, and constant returns to scale.
A focused answer to AP Microeconomics Topic 3.3, covering the long run when all inputs are variable, the long-run average total cost curve as an envelope of short-run curves, economies and diseconomies of scale, constant returns to scale, and minimum efficient scale, with worked exam-style questions.
9 min answer →

Why does a price-taking firm earn zero economic profit in the long run, and why is perfect competition efficient?

Topic 3.7 Perfect Competition: describe the characteristics of perfect competition, draw the short-run profit, loss, and break-even cases, explain the long-run zero-profit equilibrium, and show why perfect competition is efficient.
A focused answer to AP Microeconomics Topic 3.7, covering the characteristics of perfect competition, the price-taking firm's demand curve, short-run profit, loss, and break-even, the long-run zero-economic-profit equilibrium, and the allocative and productive efficiency of perfect competition, with worked exam-style questions.
12 min answer →

What output level maximizes a firm's profit, and why is the marginal revenue equals marginal cost rule universal?

Topic 3.5 Profit Maximization: explain the marginal revenue equals marginal cost rule, apply it to find the profit-maximizing output, and use the average total cost curve to measure profit or loss.
A focused answer to AP Microeconomics Topic 3.5, covering the profit-maximizing rule that marginal revenue equals marginal cost, how to find the optimal output, and how to measure total profit or loss using price and average total cost, with worked exam-style questions.
10 min answer →

How do a firm's fixed and variable costs combine into the short-run cost curves, and why are they shaped the way they are?

Topic 3.2 Short-Run Production Costs: define fixed, variable, total, marginal, and average costs, calculate each from data, and explain the shapes of the short-run cost curves and how marginal cost relates to the averages.
A focused answer to AP Microeconomics Topic 3.2, covering fixed, variable, and total cost, average fixed, average variable, average total, and marginal cost, how to calculate each, and the shapes and relationships of the short-run cost curves, with worked exam-style questions.
11 min answer →

How does a firm's output change as it adds more of a variable input, and why does the extra output eventually fall?

Topic 3.1 The Production Function: define total, marginal, and average product, explain the law of diminishing marginal returns, and relate the product curves to one another.
A focused answer to AP Microeconomics Topic 3.1, covering the production function, total product, marginal product and average product, the law of diminishing marginal returns, and how the product curves relate to one another, with worked exam-style questions.
10 min answer →

Why can a business make an accounting profit yet earn zero economic profit, and what does normal profit mean?

Topic 3.4 Types of Profit: distinguish accounting profit from economic profit using explicit and implicit costs, define normal profit, and explain what positive, zero, and negative economic profit signal.
A focused answer to AP Microeconomics Topic 3.4, covering accounting versus economic profit, explicit and implicit costs, normal profit, and what positive, zero, and negative economic profit signal for entry and exit, with worked exam-style questions.
9 min answer →