Cameroon GCE A-Level Economics common mistakes
Cameroon GCE A-Level Economics · Understand the traps and how to avoid them.
When asked to calculate opportunity cost from a production possibility frontier (PPF), the candidate reads the absolute quantities of the two goods at two points and subtracts them, instead of computing the ratio of the change in one good to the change in the other along the frontier.
The candidate confuses opportunity cost with a simple difference in output. They have memorised 'opportunity cost is what you give up' but not the operational rule that it is a rate of transformation: the number of units of one good sacrificed per additional unit of the other.
What to do instead
Practise the formula: opportunity cost of one more unit of X = (loss of Y)/(gain in X) between two points on the PPF. Work through at least five numerical PPF tables, including one where the PPF is bowed out and one where it is a straight line, and state the answer as 'x units of Y per unit of X'. Always write the ratio before simplifying, so the direction of the trade-off is visible.
When a question asks for the effect of a price change on total revenue, the candidate answers from the direction of the price change alone ('price rises, so revenue rises') without first classifying the good's price elasticity of demand.
Candidates learn the total revenue rule as a separate fact and fail to link it to elasticity. Under exam pressure they default to the intuitive but wrong assumption that a higher price always raises revenue.
What to do instead
Before writing anything about revenue, compute or classify elasticity (elastic, inelastic, unit elastic) and then apply the rule: if demand is elastic, a price rise reduces total revenue; if inelastic, a price rise increases total revenue; if unit elastic, revenue is unchanged. Train with a table of five price changes and predicted revenue movements, and in each answer write the elasticity classification first, then the revenue conclusion.
When drawing a diagram of a market with a tax, subsidy, price ceiling or price floor, the candidate shifts the wrong curve or places the intervention on the wrong side of equilibrium, then reads a quantity and price that contradict the written explanation.
The candidate memorises the shape of the diagram but not which curve the policy acts on. For example, they shift demand for a producer tax, or draw a price ceiling above equilibrium.
What to do instead
Adopt a fixed routine for every intervention diagram: (1) identify whether the policy acts on buyers or sellers; (2) shift supply for a tax or subsidy on producers, demand for one on consumers; (3) draw the ceiling below and the floor above the free-market equilibrium; (4) mark the new quantity and the price paid by buyers and received by sellers; (5) check that the written sentence matches the labels. Redraw each of the four interventions from memory three times.
In consumer theory questions, the candidate states that a consumer maximises utility where total utility is highest or where marginal utility is zero, instead of where the ratio of marginal utilities equals the ratio of prices (MUx/Px = MUy/Py).
The candidate conflates the single-good utility maximum (where MU = 0) with the two-good constrained optimum. They also confuse the indifference curve tangency condition with the budget line alone.
What to do instead
Learn the equimarginal principle as a sentence: utility is maximised when the last franc spent on each good yields the same marginal utility per franc. Practise numerical examples where MUx/Px > MUy/Py and state which good the consumer should buy more of. On the indifference-curve diagram, always draw the budget line and the highest attainable indifference curve tangent to it, and label the tangency as MRS = Px/Py.
When explaining why a firm shuts down in the short run, the candidate says the firm exits when price falls below average total cost, rather than when price falls below average variable cost.
The candidate remembers 'firms leave when they make a loss' but not the distinction between fixed and variable costs. They do not see that in the short run fixed costs are sunk and continue whether or not the firm produces.
What to do instead
Write the shutdown rule as an inequality: shut down if P < AVC; continue in the short run if AVC ≤ P < ATC, accepting losses smaller than fixed costs. Draw the AVC, ATC and MC curves and shade the region where production continues at a loss. Test understanding with a numerical table of output, TVC, TFC and price, and identify the shutdown point explicitly.
When comparing market structures, the candidate writes that a perfectly competitive firm faces a downward-sloping demand curve, or that a monopolist has no supply curve but still produces where P = MC, mixing the profit-maximisation conditions of the two models.
The candidate memorises labels ('price taker', 'price maker') without attaching them to the correct marginal revenue curve. They apply the P = MC rule universally instead of MR = MC.
What to do instead
Build a comparison table with rows for demand curve slope, MR curve, profit-maximising condition, long-run profit and efficiency. State the universal rule MR = MC, then note that for a price taker P = MR so the rule becomes P = MC, while for a monopolist P > MR so price exceeds MC. Draw both diagrams side by side and mark the deadweight loss triangle on the monopoly diagram.
When asked to evaluate government intervention to correct a negative externality, the candidate only describes the tax or subsidy and asserts that it 'makes the market efficient', without identifying the marginal social cost and marginal social benefit curves or discussing the size of the tax and its unintended effects.
Candidates learn intervention as a list of instruments and treat 'government fixes it' as a conclusion. They do not practise the diagram that shows the divergence between private and social cost, so they cannot judge whether the intervention is correctly sized.
What to do instead
For every externality answer, draw the MSC, MPC, MSB and MPB curves, mark the free-market quantity where MPC = MPB and the socially optimal quantity where MSC = MSB, and show the deadweight loss. Then evaluate: is the tax set equal to marginal external cost, can the regulator measure that cost, what are the effects on output, employment and competitiveness, and would tradable permits or regulation work better? End with a judgement, not a description.
When calculating national income or the multiplier, the candidate adds transfer payments and second-hand sales to GDP, or uses the marginal propensity to save instead of the marginal propensity to consume in the multiplier formula.
The candidate memorises the expenditure approach as 'C + I + G + X − M' but not the boundary of what counts as production. In the multiplier they confuse the two propensities because both are fractions summing to one.
What to do instead
Learn the inclusion test: only currently produced final goods and services count; exclude transfers, second-hand goods, intermediate goods and purely financial transactions. For the multiplier, write k = 1/(1 − MPC) = 1/MPS = 1/(MPS + MPT + MPM) and always substitute the marginal propensity to withdraw, not to consume, when the economy is open or taxed. Work numerical examples with an open economy and check the answer against the size of the initial injection.
When explaining inflation or its remedies, the candidate treats 'inflation' as a single phenomenon and prescribes one policy (usually raising interest rates) regardless of whether the cause is demand-pull, cost-push or imported.
Candidates revise inflation as a definition and a list of costs, not as a set of distinct causal mechanisms with different policy implications. They also overlook the open-economy channel in Cameroon, where import prices and the CFA franc peg matter.
What to do instead
Classify the cause first: demand-pull (shift AD left with contractionary fiscal or monetary policy), cost-push (incomes policy, supply-side measures, careful about a wage-price spiral), imported (exchange-rate and trade policy, limited by the peg). For each cause, name one policy that works and one that would worsen the problem, and explain why. Apply this to a Cameroonian example such as fuel or food price shocks.
When answering a question on the balance of payments or exchange rates, the candidate records the current account and capital account entries with the wrong sign, or claims that a depreciation always improves the trade balance.
Candidates memorise 'credit is inflow, debit is outflow' but do not apply it consistently to a numerical transaction. They also omit the Marshall-Lerner condition and the J-curve, so they assert an unconditional improvement.
What to do instead
Practise classifying ten transactions (exports, imports, remittances, foreign direct investment, portfolio flows, central bank reserves) into the correct account with the correct sign, and verify that the balance of payments sums to zero. For depreciation, state the Marshall-Lerner condition (sum of export and import demand elasticities exceeds one) and the J-curve time lag before concluding that the trade balance improves.