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S4 Economics Market Structure Practice Paper 3 | Efficiency, Natural Monopoly and Cartels – 10 Questions with Answers
S4 Economics Market Structure Practice Paper 3 | Efficiency, Natural Monopoly and Cartels – 10 Questions with Answers
The third set of ten market structure questions, from productive and allocative efficiency and natural monopoly to concentration ratios, HHI, monopoly pricing and cartel stability.
Direct answers This paper has 10 questions covering productive and allocative efficiency, natural monopoly, concentration ratios and HHI, monopoly pricing and the stability of cartels; suggested time is 20 minutes.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 minutes |
| Difficulty mix | Foundation 3 · Intermediate 4 · Challenge 2 · Error redo 1 |
| Chapter | S4 Economics: Market Structure |
| Level | S4 (DSE) |
02 Questions (10 items)
- FoundationAt what level of output does productive efficiency require a firm to produce?
- FoundationWhat does allocative efficiency require of price and marginal cost?
- FoundationHow does a natural monopoly arise?
- IntermediateFive firms have market shares of 40%, 25%, 15%, 12% and 8%. What is the three-firm concentration ratio?
- IntermediateContinuing from the previous question, what is the Herfindahl-Hirschman Index (HHI)?
- IntermediateDemand is P = 100 – 2Q and marginal cost is constant at 20. Find the profit-maximising output and price of the monopolist.
- IntermediateFree gifts, advertising and after-sales service belong to which type of competition?
- ChallengeWhy is a cartel agreement to restrict output and raise price often hard to maintain?
- ChallengeWhat efficiency consequence follows when a monopolist sets price above marginal cost?
- Error redoWhat is wrong with the claim that decisions of firms in an oligopoly do not affect one another?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | At the lowest point of average cost. | Using the least resources for the same output is what makes production efficient. |
| 2 | Price equals marginal cost (P = MC). | The price consumers are willing to pay exactly equals the cost of producing one more unit. |
| 3 | Economies of scale persist over the relevant range of output, so one supplier has the lowest cost. | Fixed costs for electricity grids and water pipes are so high that duplicating them is uneconomic. |
| 4 | 80%. | Add only the three largest: 40 + 25 + 15. |
| 5 | 2,658. | 1,600 + 625 + 225 + 144 + 64. |
| 6 | Q = 20, P = 60. | MR = 100 – 4Q; setting MR = MC gives Q = 20, and substituting into demand gives P = 60. |
| 7 | Non-price competition. | It wins customers without changing the list price, and is common in oligopoly. |
| 8 | Members have an incentive to raise output secretly, and once one breaks the agreement the price falls back. | Restricting output to raise price depends on trust, but raising output privately captures the profit for one firm. |
| 9 | Output is below the socially optimal level, creating allocative inefficiency (deadweight loss). | Units that buyers would pay more for than they cost are never traded. |
| 10 | An oligopoly has few interdependent firms; if one changes price or output, the others must respond. | This is exactly why oligopoly is analysed with game theory. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.
