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S4 Economics Practice Paper: Basic Concepts, Demand and Supply, Elasticity, Market Intervention, Production and Costs (100 marks)
Economics
24 parts on opportunity cost, demand and supply, elasticity, price controls, per-unit tax, production and cost curves, with all values checked by code and full marking points.
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Paper details S4 Economics practice paper with 6 sections and 24 parts on opportunity cost, demand and supply, elasticity, price controls, taxes, production and cost curves.
Section A: Basic Economic Concepts (20 marks)
Show working and units in all calculations.
| # | Question | Answer and marking notes |
|---|---|---|
| 1 | Chan’s weekend options: tutoring worth $480 in exam gain, a job paying $420, volunteering at $0. (a) If he picks tutoring, what is the opportunity cost? (b) What if the job pays $520? (c) Define opportunity cost. | Answer: (a) $420, the value of the best option given up. (b) Take the job: its value $520 exceeds the tutoring gain $480, so tutoring would cost $520. (c) Opportunity cost is the value of the highest-valued alternative forgone. (Marking: 1 for (a), 1 for choice and 1 for reason in (b), 1 for the definition, 1 for correct units) |
| 2 | Marginal benefits of an activity are $30, $24, $18 and $12; marginal cost is a constant $8 per unit. (a) How many units should be undertaken? (b) Find the total net benefit. (c) Should the fourth unit be undertaken? Explain. | Answer: (a) 4 units. (b) Total benefit 84, total cost 32, total net benefit $52. (c) Yes: marginal benefit $12 still exceeds marginal cost $8, adding $4 to net benefit. (Marking: 1 for (a), 2 for (b), 1 for the decision and 1 for the comparison) |
| 3 | Match each factor of production (labour, land, capital, entrepreneurship) with its reward (wages, rent, interest, profit). (a) State the four pairs. (b) Explain how entrepreneurship differs from the other three. | Answer: (a) Labour yields wages, land yields rent, capital yields interest, entrepreneurship yields profit. (b) Entrepreneurship organises the other three factors, bears risk and makes decisions; profit is an uncertain residual that can be negative, while wages, rent and interest are contractual. (Marking: 1 per pair, 1 for the explanation) |
| 4 | Classify as positive or normative: (1) a higher minimum wage makes some low-skilled workers jobless; (2) the government should raise the minimum wage; (3) inflation was two per cent last year; (4) the government should pay more allowances. State the criterion. | Answer: (1) positive, (2) normative, (3) positive, (4) normative. Criterion: a positive statement can be tested against facts, while a normative statement involves value judgement, often with should, and cannot be settled by facts alone. (Marking: 1 per item, 1 for the criterion) |
Section B: Demand and Supply (16 marks)
Distinguish shifts of a curve from movements along it.
| # | Question | Answer and marking notes |
|---|---|---|
| 5 | The price of a good falls from $20 to $16 and quantity demanded rises from 40 to 52 units. (a) Find the percentage change in quantity demanded. (b) Find the percentage change in price. (c) State the direction of the relationship. | Answer: (a) (52 – 40) / 40 x 100 = 30 per cent. (b) (16 – 20) / 20 x 100 = -20 per cent. (c) Price falls while quantity demanded rises: they move in opposite directions, as the law of demand predicts. (Marking: 1 each for (a) and (b), 1 for direction and 1 for the law) |
| 6 | In a market, Qd = 120 – 3P and Qs = 20 + 2P. (a) Find the equilibrium price and quantity. (b) At a price of $30, state what occurs and by how much. | Answer: (a) Set Qd = Qs: 120 – 3P = 20 + 2P, so P = $20 and Q = 60 units. (b) At $30, Qd = 30 and Qs = 80, so there is a surplus of 50 units and price tends to fall. (Marking: 1 for equilibrium price and 1 for quantity; 1 for the situation and 1 for the size) |
| 7 | State whether each event shifts a supply curve left or right: (1) wages of workers rise; (2) production technology improves; (3) producers expect a large price rise; (4) more firms enter. Give the direction for each. | Answer: (1) left, higher costs reduce supply; (2) right, better technology raises productivity; (3) left, expected higher prices cut supply now; (4) right, market supply is the sum of firms. (Marking: 1 per item with a correct reason) |
| 8 | Demand is P = 60 – 2Q and the market price is $20. (a) Find the equilibrium quantity. (b) Compute consumer surplus. (c) Explain what consumer surplus means. | Answer: (a) At $20, 60 – 2Q = 20 gives Q = 20 units. (b) Consumer surplus = half x base x height = half x 20 x (60 – 20) = $400. (c) It is the excess of what consumers are willing to pay over what they actually pay. (Marking: 1 for (a), 1 for the formula and 1 for the value in (b), 1 for (c)) |
Section C: Elasticity (16 marks)
State clearly when elasticity is quoted in absolute value.
| # | Question | Answer and marking notes |
|---|---|---|
| 9 | Price rises from $10 to $12 and quantity demanded falls from 50 to 40. (a) Compute the price elasticity of demand by the percentage method. (b) Classify the elasticity. (c) To raise total revenue, should the firm raise or cut price? | Answer: (a) Quantity falls 20 per cent and price rises 20 per cent, so elasticity is 1 in absolute value. (b) Unit elastic. (c) Total revenue is unchanged by the price change, so raising or cutting price has the same effect on revenue. (Marking: 1 each for the two percentages and 1 for the value, 0.5 for the label, 0.5 for (c)) |
| 10 | Price rises from $10 to $12 and quantity falls from 50 to 38. (a) Compute total revenue before and after. (b) Compute the elasticity and classify it. (c) Explain the link between revenue and elasticity. | Answer: (a) Before: $10 x 50 = $500; after: $12 x 38 = $456. (b) Quantity falls 24 per cent while price rises 20 per cent, so elasticity is about 1 and demand is elastic. (c) With elastic demand price and revenue move in opposite directions, so the price rise cuts revenue from $500 to $456. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
| 11 | Income rises from $20000 to $22000 and quantity demanded rises from 100 to 130. (a) Compute income elasticity. (b) Classify the good as necessity, luxury or inferior. (c) State the classification when elasticity is negative. | Answer: (a) Quantity rises 30 per cent and income rises 10 per cent, so income elasticity is 3. (b) Above one, so it is a luxury. (c) A negative value means demand falls as income rises, an inferior good; a value between zero and one means a necessity. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
| 12 | The price of X rises 10 per cent. Demand for Y rises 25 per cent; demand for Z falls 15 per cent. (a) Compute both cross elasticities with respect to X. (b) Classify each good. (c) Give an example of substitutes. | Answer: (a) Y with X: 25 over 10 = 2.5; Z with X: minus 15 over 10 = -1.5. (b) Y has positive cross elasticity so it is a substitute; Z has negative cross elasticity so it is a complement. (c) Cola and lemonade: a cola price rise lifts lemonade demand, a positive cross elasticity. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
Section D: Market Intervention (16 marks)
Support every conclusion with figures.
| # | Question | Answer and marking notes |
|---|---|---|
| 13 | Qd = 180 – 4P and Qs = 20 + 4P. A price ceiling of $15 is imposed. (a) Find the equilibrium price. (b) Find the shortage created. (c) State two non-price rationing methods that may appear. | Answer: (a) Setting Qd = Qs gives P = $20. (b) At $15, below equilibrium, Qd = 120 and Qs = 80, so the shortage is 40 units. (c) Queuing, ration coupons, or seller rationing by preference. (Marking: 1 for (a), 2 for (b), 1 for (c)) |
| 14 | Qd = 200 – 4P and Qs = 24 + 4P. A price floor of $26 is set. (a) Find the equilibrium price. (b) Find the surplus created. (c) If the government buys the whole surplus, what is the outlay? | Answer: (a) P = $22. (b) At $26, above equilibrium, Qd = 96 and Qs = 128, so the surplus is 32 units. (c) Outlay = $26 x 32 = $832. (Marking: 1 for (a), 1 for (b), 2 for (c)) |
| 15 | Qd = 200 – 4P and Qs = 24 + 4P, and a per-unit tax of $6 is levied on sellers. (a) Find the new price and quantity. (b) Find tax revenue. (c) Find the consumer share per unit and the deadweight loss. | Answer: (a) Supply becomes 24 + 4(P – 6); setting Qd = Qs gives P = $25 and Q = 100 units. (b) Revenue = $6 x 100 = $600. (c) Consumers bear $25 – $22 = $3 per unit, half the tax, and producers bear the rest; deadweight loss = half x 6 x (112 – 100) = $36. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
| 16 | Describe in one sentence the immediate market effect of each: (1) an import quota; (2) an ad valorem tax; (3) a production subsidy; (4) a price ceiling. | Answer: (1) A quota caps imports, cutting local supply and raising price; (2) an ad valorem tax is a percentage of price, cutting supply and raising price while quantity falls; (3) a subsidy lowers costs, raising supply and quantity while price falls; (4) a ceiling below equilibrium creates a shortage and non-price rationing. (Marking: 1 per item) |
Section E: Production and Division of Labour (16 marks)
Work out the output table yourself.
| # | Question | Answer and marking notes |
|---|---|---|
| 17 | A firm hires 1 to 4 workers with total output 10, 26, 39, 45 units. (a) Compute average product for each. (b) Compute marginal product. (c) State the worker number with the highest average product. | Answer: (a) Average products are 10.0, 13.0, 13.0, 11.25. (b) Marginal products are 10, 16, 13, 6. (c) Workers 2 and 3 tie at the highest average product of 13.0. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
| 18 | Using the output table above: (a) from which worker does diminishing marginal returns begin? (b) Explain with the numbers. (c) State the condition for the law to hold. | Answer: (a) From worker 3. (b) Marginal product falls from 16 units for worker 2 to 13 for worker 3, then to 6, so each extra worker adds less. (c) At least one factor, such as the plant, must be fixed and technology unchanged. (Marking: 1 for (a), 2 for (b), 1 for (c)) |
| 19 | Give three reasons why division of labour raises productivity, and one everyday example of division of labour. | Answer: three reasons: workers repeat one task and gain skill; time lost switching tasks and tools is saved; specialised machines and matching workers to strengths become possible. Example: a restaurant kitchen splits chopping, cooking and plating, so service is faster. (Marking: 1 per reason, 1 for the example) |
| 20 | Classify each as economies or diseconomies of scale: (1) bulk buying earns discounts; (2) more management layers slow communication; (3) large efficient machines spread fixed costs; (4) too many staff cause coordination problems and waste. | Answer: (1) economies, lower input cost; (2) diseconomies, slower management; (3) economies, lower average fixed cost; (4) diseconomies, higher coordination cost. (Marking: 1 per item) |
Section F: Costs and Firm Decisions (16 marks)
Label cost types clearly and give numerical answers.
| # | Question | Answer and marking notes |
|---|---|---|
| 21 | A firm has fixed cost $600 and variable costs $400, 900, 1500 at outputs 10, 20 and 30 units. (a) Find total cost at each output. (b) Find average fixed cost. (c) Find average variable cost and average total cost. | Answer: (a) Total costs are $1000, 1500, 2100. (b) Average fixed costs are $60.0, 30.0, 20.0. (c) Average variable costs are $40.0, 45.0, 50.0 and average total costs are $100.0, 75.0, 70.0. (Marking: 1 for (a), 1 for (b), 2 for (c)) |
| 22 | Using the table: (a) find marginal cost from 10 to 20 units and from 20 to 30 units. (b) Compare it with average cost and explain why average cost falls. (c) If the next 10 units cost $70, does average cost rise or fall? | Answer: (a) First step: (1500 – 1000) over 10 = $50.0; second step: (2100 – 1500) over 10 = $60.0. (b) Both marginal costs are below the average costs of $100.0 and $75.0, pulling the average down. (c) Marginal cost $70 exceeds the current average $70.0, so average cost rises. (Marking: 2 for (a), 1 for (b), 1 for (c)) |
| 23 | A firm produces 30 units at a price of $45; average variable cost is $50 and fixed cost is $600. (a) Should it keep producing or shut down? (b) Compute the loss in each case. (c) Explain the rule used. | Answer: (a) Shut down. (b) Producing loses fixed cost plus (average variable cost minus price) times output = $600 + ($50 – $45) x 30 = $750, while shutting down loses only the fixed cost $600. (c) Price $45 is below average variable cost $50, so each unit adds to the loss. (Marking: 1 for (a), 2 for (b), 1 for (c)) |
| 24 | A price taker sells at $70 with MC = 10 + 2Q and TC = 300 + 10Q + Q squared. (a) Find the profit-maximising output. (b) Find total revenue, total cost and profit. (c) State the rule applied. | Answer: (a) As a price taker MR equals price $70; setting MR = MC gives 70 = 10 + 2Q, so Q = 30 units. (b) Revenue = $70 x 30 = $2100; total cost = 300 + 10 x 30 + 30 squared = $1500; profit = $2100 – $1500 = $600. (c) Produce while marginal revenue exceeds marginal cost, stopping at MR = MC. (Marking: 1 for (a), 2 for (b), 1 for (c)) |
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