S4 Economics Paper: Production, Firm Costs And Market Structure (100 Marks)

S4 Economics Paper: Production, Firm Costs and Market Structure (100 marks)

2026-11-11

S4 Economics – production and market structure

S4 economics practice paper: production and firm costs, accounting and economic profit, market concentration, monopoly pricing and economies of scale, with full answers.

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Paper details　S4 economics practice paper on production, firm costs, accounting and economic profit, market concentration, monopoly pricing, economies of scale and minimum wage policy.

Part A Question 1: Revenue, Cost and Profit

Study the firm data below and answer all sub-questions.

#	Question	Answer and marking notes
1	(a) A manufacturer produces and sells 3 000 units of an electronic part each month at 15 dollars per unit. Find the total revenue for the month.	Answer: 45 000 dollars. Total revenue = quantity x price = 3 000 x 15 = 45 000 dollars. Marking: value 1, currency unit 1.
2	(b) Raw material cost is 9 000 dollars, the firm employs 3 workers at 9 000 dollars each per month, and rent is 6 000 dollars. Find the total cost for the month.	Answer: 42 000 dollars. Total wages = 3 x 9 000 = 27 000 dollars; total cost = 9 000 + 27 000 + 6 000 = 42 000 dollars. Marking: wages 1, summation 1, unit 1.
3	(c) Using the data above, find the profit for the month.	Answer: 3 000 dollars. Profit = total revenue – total cost = 45 000 – 42 000 = 3 000 dollars. Marking: formula 1, value 1, unit 1.
4	(d) Find the profit margin as a percentage of total revenue, correct to 2 decimal places.	Answer: 6.67 per cent. Profit margin = 3 000 / 45 000 x 100% = 6.67%. Marking: formula 2, value 1, per cent sign 1.

Part A Question 2: Accounting Profit, Economic Profit and Average Cost

Mr Chan owns and runs a small shop by himself.

#	Question	Answer and marking notes
5	(a) The shop records an accounting profit of 15 000 dollars. By running the shop, Mr Chan gives up a paid job that would pay 20 000 dollars a month. Find the economic profit and state which type of cost this salary represents.	Answer: economic profit is -5 000 dollars, that is an economic loss of 5 000 dollars. The 20 000 dollars is an implicit cost, being the opportunity cost of the owner labour. 15 000 – 20 000 = -5 000 dollars. Marking: implicit cost 1, calculation 1, conclusion of economic loss 1.
6	(b) Fixed cost is 8 000 dollars a month and output is 500 units. Find the average fixed cost.	Answer: 16 dollars. Average fixed cost = 8 000 / 500 = 16 dollars. Marking: formula 1, value and unit 1.
7	(c) Unit variable cost is 12 dollars. At an output of 500 units, find the average total cost.	Answer: 28 dollars. Total cost = 8 000 + 12 x 500 = 14 000 dollars; average total cost = 14 000 / 500 = 28 dollars. Marking: 1 mark for a fully correct answer.
8	(d) If output rises to 800 units, find the new average fixed cost and the new total cost.	Answer: average fixed cost 10 dollars (8 000 / 800); total cost 17 600 dollars (8 000 + 12 x 800). Marking: average fixed cost 1, total cost 1.

Part B Question 3: Market Concentration and Market Structure

An industry has five firms with market shares of 35%, 25%, 20%, 10% and 10% respectively.

#	Question	Answer and marking notes
9	(a) Calculate the four-firm concentration ratio (CR4).	Answer: 90%. CR4 = 35% + 25% + 20% + 10% = 90%. Marking: formula 2, value 1.
10	(b) Calculate the Herfindahl-Hirschman Index (HHI) on a scale from 0 to 10 000.	Answer: 2 450. HHI = 35^2 + 25^2 + 20^2 + 10^2 + 10^2 = 1 225 + 625 + 400 + 100 + 100 = 2 450. Marking: squares up to 2, summation 1, value 1.
11	(c) Based on the data, identify the market structure of this industry and give two reasons.	Answer: oligopoly. Reason one: CR4 of 90% shows that a few firms dominate the market. Reason two: each of the five firms is sizeable, so pricing decisions must take rivals reactions into account (mutual interdependence). Marking: identification 1, each reason 1.
12	(d) If the second and third largest firms merge, find the new CR4 and HHI, and discuss the likely effects of the merger on prices and consumers.	Answer: the merged firm holds 45%, so CR4 = 35% + 45% + 10% + 10% = 100% and HHI = 35^2 + 45^2 + 10^2 + 10^2 = 1 225 + 2 025 + 100 + 100 = 3 450. Effects: greater pricing power, output may fall and price may rise; consumers face fewer choices and weaker bargaining power; the Competition Commission may review the merger under the Competition Ordinance. Marking: new share 1, CR4 1, HHI 2, each effect 1.

Part B Question 4: Output and Pricing of a Monopolist

A monopolist faces the demand curve P = 120 – 2Q and a constant marginal cost of 20 dollars.

#	Question	Answer and marking notes
13	(a) Derive the marginal revenue function of the firm.	Answer: total revenue TR = P x Q = (120 – 2Q)Q = 120Q – 2Q squared; marginal revenue MR = 120 – 4Q. Marking: TR function 2, differentiation 1, MR function 1.
14	(b) Find the profit-maximising output.	Answer: 25 units. Profit is maximised where MR = MC: 120 – 4Q = 20, so 4Q = 100 and Q = 25. Marking: condition 1, algebra 1, value 1.
15	(c) Find the price and total revenue at that output.	Answer: price 70 dollars (P = 120 – 2 x 25 = 70); total revenue 1 750 dollars (70 x 25). Marking: price 2, total revenue 2.
16	(d) Find the profit of the firm and explain why the profit-maximising output differs from the revenue-maximising output.	Answer: profit = 1 750 – 20 x 25 = 1 250 dollars. Revenue is maximised where MR = 0, that is 120 – 4Q = 0 and Q = 30, giving P = 60 dollars and TR = 1 800 dollars; total cost is 600 dollars, so profit is only 1 200 dollars, which is below 1 250 dollars. Beyond 25 units marginal cost exceeds marginal revenue, so profit falls. Marking: profit 2, revenue-maximising output 1, comparison 1, explanation 1.

Part C Question 5: Economies of Scale and Minimum Efficient Scale

The long-run average cost of a firm is 40 dollars at 1 000 units, 32 dollars at 2 000 units and 35 dollars at 4 000 units.

#	Question	Answer and marking notes
17	(a) By what percentage does long-run average cost fall when output rises from 1 000 to 2 000 units? What is this phenomenon called?	Answer: a fall of 20%. Calculation: (40 – 32) / 40 x 100% = 20%. The phenomenon is called economies of scale. Marking: formula 3, value 2, name 3.
18	(b) By what percentage does long-run average cost change when output rises from 2 000 to 4 000 units? Explain the cause.	Answer: a rise of 9.375%. Calculation: (35 – 32) / 32 x 100% = 9.375%. Cause: diseconomies of scale, as a very large output raises management layers and coordination work, pushing up communication and supervision cost per unit. Marking: formula 3, value 2, explanation 3.
19	(c) If market demand is 6 000 units, find the minimum efficient scale, the number of firms that can operate at that scale, and state the implication for market structure.	Answer: the minimum efficient scale is 2 000 units, the output at which long-run average cost is lowest. The market can support 6 000 / 2 000 = 3 firms. Implication: only a few large firms can operate efficiently, new entrants cannot compete at a small scale, so the market tends towards oligopoly. Marking: minimum efficient scale 3, number of firms 2, implication 3.

Part C Question 6: Analysis of Minimum Wage Policy

A cleaning company employs 200 workers, each working 160 hours a month. The statutory minimum wage rises from 40 to 45 dollars per hour.

#	Question	Answer and marking notes
20	(a) Find the increase in the monthly wage bill of the company, in dollars and as a percentage.	Answer: original wage bill = 40 x 200 x 160 = 1 280 000 dollars; new wage bill = 45 x 200 x 160 = 1 440 000 dollars; an increase of 160 000 dollars, that is 12.5% (160 000 / 1 280 000 x 100%). Marking: the two totals 2 each, difference 2, percentage 2.
21	(b) If the company raises the price of each service from 50 to 52 dollars while sales stay at 40 000 items a month, find the extra revenue and judge whether it fully offsets the rise in the wage bill. If not, find the number of workers that must be cut.	Answer: extra revenue = 2 x 40 000 = 80 000 dollars, which falls short of the 160 000 dollar rise; the shortfall is 80 000 dollars. At the new wage each worker earns 45 x 160 = 7 200 dollars a month; 80 000 / 7 200 = 11.11, so 12 workers must be cut. Marking: extra revenue 2, judgement 2, monthly wage 2, number of workers 2.
22	(c) Discuss the effects of a higher minimum wage on low-skilled workers, employer costs and consumers.	Expected points: for low-skilled workers, those employed earn more, but some may be laid off or moved to part-time work as costs rise, so there is a trade-off; for employers, wage costs rise and marginal cost shifts up, which may reduce hiring, speed up automation or lead to higher prices; for consumers, prices may rise and choice may shrink if costs are passed on. A good conclusion notes that the net effect depends on the elasticity of demand for labour and the ability of the firm to pass on costs. Marking: each of the three angles 2, conclusion 2.

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