Practice Market Structures: Economics Unit 3.
This unit covers perfect competition, monopoly, oligopoly and monopolistic competition — essential concepts for Economics. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers perfect competition, monopoly, oligopoly and monopolistic competition — essential concepts for Economics. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Perfect Competition
Perfect competition is a market structure with many buyers and sellers, identical products, and no barriers to entry. In the long run, economic profit is zero because firms enter or exit until price equals minimum average total cost. Firms are price takers — they have no control over the market price.
Key Points
- P = MR = MC at profit-maximizing output
- Long-run equilibrium: P = minimum ATC (zero economic profit)
- Many firms, identical (homogeneous) products, perfect information
- Short run: firms can earn profit, loss, or break even
A wheat farm sells wheat at the market price of $5 per bushel. At 1,000 bushels, MC = $5 and ATC = $4. Is the firm making a profit, and should it produce this output?
Since P ($5) = MC ($5), the firm is at its profit-maximizing output — this is the rule to identify the correct quantity. Since P ($5) > ATC ($4), the firm earns an economic profit of $1 per bushel, or $1,000 total. In the long run, new firms will enter, supply increases, price falls to $4, and economic profit returns to zero.
2 Monopoly
A monopoly is a single seller with no close substitutes and high barriers to entry, giving it significant price-setting power. The monopolist maximizes profit by producing where MR = MC, but unlike perfect competition, price exceeds MR because the demand curve is downward sloping. Monopolies create deadweight loss because output is restricted below the socially optimal level.
Key Points
- Profit-maximizing rule: produce where MR = MC, then find price on demand curve
- P > MR = MC at equilibrium (price exceeds marginal cost)
- Barriers to entry: patents, resource control, government franchise
- Deadweight loss exists; monopoly is allocatively inefficient
A monopolist faces demand P = 20 – 2Q. At Q = 4, MC = $4, MR = $4, and ATC = $6. What price does the firm charge, and is it earning a profit or a loss?
The firm produces Q = 4 because MR = MC = $4 — that is the profit-maximizing quantity. To find price, plug Q = 4 into the demand equation: P = 20 – 2(4) = $12. Since P ($12) > ATC ($6), the firm earns an economic profit of $6 per unit, or $24 total.
3 Oligopoly
An oligopoly has a few large firms that are mutually interdependent — each firm's decisions affect and are affected by rivals. Key models include the kinked demand curve (explains price rigidity) and game theory/prisoner's dilemma (explains why firms may collude or cheat). Collusion to act as a monopoly is illegal but firms may form cartels.
Key Points
- Few firms, high barriers to entry, differentiated or identical products
- Mutual interdependence: firms consider rivals' reactions before deciding
- Kinked demand curve: rivals match price cuts but not price increases, creating a gap in the MR curve
- Nash equilibrium in prisoner's dilemma: both firms cheat (dominant strategy)
Two airlines both charge $300. If one airline cuts to $250, the other will match. If one raises to $350, the other will not follow. Using the kinked demand model, explain why the price stays at $300 even if costs change.
Above $300, demand is elastic because rivals won't follow a price increase, so customers switch away. Below $300, demand is inelastic because rivals match the cut, so no customers are gained. This creates a gap (discontinuity) in the MR curve at the current quantity. As long as MC stays within that gap, the profit-maximizing output and price remain unchanged, explaining price stickiness.
4 Monopolistic Competition
Monopolistic competition has many firms selling differentiated products with low barriers to entry, giving each firm slight price-setting power in the short run. Like perfect competition, long-run economic profit is zero — entry by new firms shifts each firm's demand curve left until P = ATC. Unlike perfect competition, the firm does not produce at minimum ATC, resulting in excess capacity.
Key Points
- Many firms, differentiated products (branding, quality, location), low barriers
- Short run: can earn profit or loss; profit-maximize at MR = MC
- Long run: P = ATC (zero economic profit), but P > MC (still allocatively inefficient)
- Excess capacity: firms produce less than the output at minimum ATC
A local coffee shop earns economic profit in the short run. Describe what happens in the long run to price, quantity, and economic profit.
Economic profit attracts new coffee shops to enter the market, which increases the number of substitutes available to consumers. Each existing firm's demand curve shifts left (and becomes more elastic) as customers have more choices. This continues until price equals ATC, economic profit falls to zero, and no further entry occurs — the long-run equilibrium.
Questions, answered.
What is Market Structures?
Market Structures is Unit 3 of Economics, covering perfect competition, monopoly, oligopoly and monopolistic competition.
How to study for Economics Unit 3?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 28+ review questions across 5 different game modes.