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Junior Economist Qualification study materials
Junior Economist Qualification study resources

Junior Economist Qualification: Microeconomics

Junior Economist Qualification · Work through your exam, one topic at a time.

All guide sections

Microeconomics

Microeconomics on the Junior Economist Qualification tests how prices coordinate scarce resources across consumers, firms, and markets, and how taxes, market power, and intervention change welfare. Questions typically combine elasticity calculations, cost-curve reasoning, market-structure predictions, and incidence or deadweight-loss analysis described in words.

Core rules and concepts

  • Consumer choice: utility is maximized where the marginal rate of substitution equals the price ratio, MRS = Px/Py. Income changes shift the budget line; a price change rotates it.
  • Elasticity: use the midpoint formula for price elasticity of demand, Ed = (ΔQ/ΔP)·((P1+P2)/(Q1+Q2)), and compare |Ed| with 1. Supply elasticity uses the same logic.
  • Competitive firm: profit maximization sets P = MC. Shutdown compares price with average variable cost, not average total cost. Long-run equilibrium has P = minimum ATC.
  • Monopoly: set MR = MC, then read price from demand. MR lies below demand because extra output lowers price on all units.
  • Welfare: consumer surplus is the area below demand and above price; producer surplus is above supply and below price. A tax creates deadweight loss unless demand or supply is perfectly inelastic.

Worked example

Demand Qd = 100 − 2P and supply Qs = 20 + 3P. Free-market equilibrium: 100 − 2P = 20 + 3P, so P = 16 and Q = 68. A specific tax of 5 per unit on sellers changes supply to Qs = 20 + 3(P − 5) = 5 + 3P. New equilibrium: 100 − 2P = 5 + 3P, so P = 19 and Q = 62. Consumers pay 3 more; sellers receive 19 − 5 = 14, which is 2 less than before. Consumer incidence is 3/5 = 60% and producer incidence is 2/5 = 40%. Deadweight loss is ½ × 5 × (68 − 62) = 15.

Traps that cost marks

Do not confuse a movement along a demand curve with a shift. A tax on sellers shifts supply upward by the tax; a tax on buyers shifts demand downward. Use absolute value for demand elasticity, and remember that fixed costs do not affect short-run shutdown. Monopolies have no supply curve, and sunk costs are irrelevant to forward-looking decisions.