Cambridge O Level Economics: The mixed economic system and government intervention (2281) – Revision Notes

These are condensed notes for section 2.11 of the Cambridge O Level Economics syllabus for examination in 2026. The study guide has the fuller explanations; afterwards, test yourself with the practice questions. Course links: Cambridge O Level Economics hub, printable checklist and free 10-minute diagnostics. All numbers here are invented and illustrative. Earlier ideas are in the allocation of resources revision notes.

Definitions to learn

Term	Definition
Mixed economic system	Resources are allocated by both the private sector (price mechanism) and the government (public sector)
Maximum price	A legal limit above which a price cannot be charged
Minimum price	A legal limit below which a price cannot fall
Indirect tax	A tax on spending on goods and services, paid to the government by sellers
Subsidy	A payment from the government that lowers the cost of producing or buying a good
Regulation	Laws and rules that control how firms and consumers behave
Privatisation	Sale of state-owned assets to the private sector
Nationalisation	Transfer of private-sector firms to government ownership
Direct provision	The government supplies goods and services itself

The three price diagrams in steps

1. Draw demand and supply, mark equilibrium price and quantity.
2. Draw the controlled price as a horizontal line. A maximum price must be below equilibrium. A minimum price must be above it.
3. Read quantity demanded where the line meets demand, and quantity supplied where it meets supply.
4. Larger quantity demanded than supplied is a shortage. Larger quantity supplied than demanded is a surplus.
5. Say who gains, who loses and what the government must do next (ration, buy up, enforce).

Market	Price is	Maximum price creates	Minimum price creates
Product	Price of the good	Shortage, black market	Surplus, government buying
Labour	Wage	Labour shortage (rare)	Unemployment
Foreign exchange	Exchange rate	Excess demand for the currency, so the central bank sells it	Excess supply of the currency, so the central bank buys it

Worked reminder (maximum price, illustrative). Qd = 240 − 8P, Qs = −48 + 16P.

• Equilibrium: 288 = 24P, so P = 12, Q = 144.
• Maximum price 9: Qd = 168, Qs = 96, shortage = 72.
• Buyers would pay up to P where 240 − 8P = 96, so P = 18, which is the likely black-market price.

Worked reminder (minimum price, illustrative). Qd = 300 − 6P, Qs = −60 + 12P.

• Equilibrium: 360 = 18P, so P = 20, Q = 180.
• Minimum price 25: Qd = 150, Qs = 240, surplus = 90.
• If the government buys the surplus, cost = 25 × 90 = 2,250.

Taxes and subsidies in steps

	Indirect tax	Subsidy
Effect on supply	Shifts up (left) by the tax	Shifts down (right) by the subsidy
Market price	Rises	Falls
Quantity	Falls	Rises
Government	Gains revenue = tax × new quantity	Pays cost = subsidy × new quantity
Burden or gain	Split between consumers and producers	Split between consumers and producers
Usually aimed at	Demerit goods, external costs, revenue	Merit goods, external benefits

Key rules:

• The vertical gap between the old and new supply curve equals the tax or subsidy.
• Consumer burden per unit = new price − old price.
• Producer burden per unit = tax − consumer burden.
• The more inelastic side bears more of a tax and gains more from a subsidy.

Worked reminder (tax, illustrative). Qd = 500 − 10P, Qs = −100 + 15P.

• Equilibrium: 600 = 25P, so P = 24, Q = 260.
• Tax 5: Qs = −100 + 15(P − 5) = −175 + 15P. Then 675 = 25P, so P = 27, Q = 230.
• Consumers pay 3 more, producers bear 5 − 3 = 2. Revenue = 5 × 230 = 1,150.

Worked reminder (subsidy, illustrative). Qd = 400 − 10P, Qs = −50 + 20P.

• Equilibrium: 450 = 30P, so P = 15, Q = 250.
• Subsidy 3: Qs = −50 + 20(P + 3) = 10 + 20P. Then 390 = 30P, so P = 13, Q = 270.
• Consumers pay 2 less. Producers receive 13 + 3 = 16, which is 1 more. Cost = 3 × 270 = 810.

Other measures

Measure	Reason	Main advantage	Main drawback
Regulation	Limit harm, protect consumers, curb monopoly	Direct control	Cost of enforcing, loopholes, higher costs for firms
Privatisation	Raise efficiency, raise funds	Profit motive, lower government spending	Social aims lost, possible private monopoly
Nationalisation	Control essential or monopoly industries	Public interest first	Weak incentives, taxpayer funds losses
Direct provision	Public and merit goods are under-provided	Reaches everyone	Opportunity cost, possible waste

Opportunity cost reminder. A budget of 200 buys hospitals at 50 or colleges at 20. Three hospitals cost 150, leaving 50, which buys 2 colleges (50 / 20 is 2.5, so 2 whole). One extra hospital costs 50 / 20 = 2.5 colleges.

Must-know distinctions

• Tax versus subsidy: opposite shifts of supply, opposite effects on price and quantity.
• Shortage versus surplus: shortage comes from a maximum price, surplus from a minimum price.
• Privatisation versus nationalisation: ownership moves out of, or into, the state.
• Regulation versus direct provision: rules for private suppliers versus the government supplying the good.
• Market failure versus government failure: the first is the reason to intervene, the second is intervention that makes matters worse or costs too much.

Evaluating effectiveness

Use a short chain: aim, mechanism, result, drawback, judgement.

• Tax on a demerit good: price up, quantity down. It works best if demand is elastic and substitutes exist. If demand is inelastic, consumption barely falls but revenue is high.
• Subsidy for a merit good: price down, use rises. It works if it reaches consumers, but it costs taxpayers.
• Maximum price: helps those who get the good. Fails if the shortage is large and enforcement is weak.
• Minimum wage: helps those who stay employed. The loss of jobs is larger if labour demand is elastic.
• Regulation: targets the harm directly, but monitoring costs money and firms may pass higher costs on to buyers.
• Privatisation: may raise efficiency and bring in funds, but social aims can be lost and a private monopoly may form.
• Direct provision: reaches everyone, including those who could not pay, but every unit built has an opportunity cost.
• Judge by context: size of the gap, elasticity, cost, time lag and side effects. Do not simply list advantages and disadvantages.

Evaluation sentence frame: “This policy should work because …, but it is limited by …, so overall it is most effective when …”.

Quick self-test

1. Define a mixed economic system.
2. Qd = 120 − 4P and Qs = 6P. Find equilibrium price and quantity.
3. Using question 2, a minimum price of 15 is set. Find the surplus.
4. Using question 2, a maximum price of 10 is set. Find the shortage.
5. Labour: Ld = 500 − 25W, Ls = 100 + 15W. Find equilibrium and the unemployment created by a minimum wage of 12.
6. A tax of 4 per unit raises the market price from 25 to 27 and 60 units are sold. How much of the revenue do consumers bear?
7. A subsidy of 4 per unit cuts price from 30 to 27 and raises sales from 100 to 118. Work out what the subsidy costs taxpayers and what fraction of it consumers receive as a lower price.
8. A central bank fixes its currency at 2.5 foreign units per unit while equilibrium is 2.0, creating excess supply of 40 million. What must it spend?
9. State two drawbacks of nationalisation.
10. Give one reason a tax may fail to reduce consumption of a demerit good.

Answers

1. A system where resources are shared out through both private markets and government decisions.
2. 120 − 4P = 6P, so 120 = 10P, P = 12 and Q = 72.
3. Qd = 120 − 60 = 60, Qs = 90. Surplus = 30.
4. Qd = 120 − 40 = 80, Qs = 60. Shortage = 20.
5. 400 = 40W, so W = 10 and L = 250. At 12: Ld = 200, Ls = 280, so unemployment = 80.
6. Consumers pay 27 − 25 = 2 more per unit, so they bear 2 × 60 = 120 of the 240 revenue. Producers bear 120.
7. Cost = 4 × 118 = 472. Consumers gain 3 of the 4, so three quarters (3/4).
8. 40 million × 2.5 = 100 million foreign units, taken from reserves.
9. Any two from: weak incentives to be efficient, losses paid by taxpayers, political interference, less choice.
10. Demand is price inelastic, or there are no close substitutes, or the good is habit-forming.

Where marks are usually lost

• Setting a ceiling above equilibrium or a floor below it, which changes nothing.
• Shifting supply left for a subsidy or right for a tax.
• Saying a minimum wage creates a labour shortage: it creates unemployment, because the wage is above equilibrium.
• Giving the tax revenue as tax × old quantity instead of tax × new quantity.
• Stating the price rises by the whole tax when the burden is shared.
• Forgetting the cost to the government or taxpayers in an evaluation.
• Giving only advantages of privatisation or only drawbacks of nationalisation.
• Ending an evaluation without a judgement tied to the case.

Official syllabus

Cambridge O Level Economics 2281 syllabus for examination in 2026, published by Cambridge University Press and Assessment (Cambridge International Education), section 2.11.