Microeconomic decision-makers

• Anchor. “Scale cuts the average, not the total.” It is the single sentence that separates a correct answer on economies of scale from an ambiguous one, and the same instinct — per unit, not in total — is what makes the whole of 3.6 fall into place.
• Anchor for the seven. “All Dogs Prefer Digging Six Useful Spots” — Acceptable, Durable, Portable, Divisible, Scarce, Uniform, Stable. Silly sentences survive examination nerves better than tidy ones.
• One sentence for every wage-difference question. “A wage is high when a small supply meets a large demand; bargaining strength, discrimination and government policy then move it from there.” Open with that, apply it to the case in front of you, and the structure of the answer is already right.
• The habit these three share. Every one of them was checked by a second route: ATC two ways, productivity against the workforce, profit per unit against total profit. Two routes that agree is how you know an answer is right before anyone marks it, and it takes about fifteen seconds.
• The chapter in one line, for the walk to the examination hall. Name the decision-maker, name their constraint, follow the chain. Demand for labour is derived. A minimum wage only bites above the equilibrium. Scale cuts the average, not the total. Production is how much; productivity is how much each. And 3.7 is answered in words.

• 3.1.1 — Define money, state its two forms, and give its four functions and seven characteristics.
• 3.1.2 — Describe the role and importance of a central bank, and of commercial banks, without confusing the two.
• 3.2.1 — Explain all five influences on households' spending, saving and borrowing: income, the rate of interest, confidence, age and culture.
• 3.3.1 — Separate wage factors from non-wage factors in an individual's choice of occupation, and explain why a worker might accept lower pay.
• 3.3.2 — Explain wage determination through the demand for and supply of labour; explain trade unions and what makes their bargaining power strong or weak; explain government policy including a national minimum wage — and draw and interpret a shift in labour demand, a shift in labour supply, and a minimum wage.
• 3.3.3 — Explain the reasons for differences in wages, and how they act through skill level, economic sector, discrimination and the private-public comparison.
• 3.3.4 — Explain the causes and consequences of changes in occupational and geographical mobility of labour.
• 3.3.5 — Define the division of labour and give its advantages and disadvantages.
• 3.4.1 — Classify firms by sector and by ownership, and argue the advantages and disadvantages of small and of large firms.
• 3.4.2 — Define horizontal, vertical and conglomerate mergers, give an example of each, and argue both sides of each.
• 3.4.3 — Distinguish internal from external economies and diseconomies of scale, and draw and interpret an average total cost diagram.
• 3.5.1 — Explain the influences on the demand for factors of production.
• 3.5.2 — Explain why a firm chooses labour-intensive or capital-intensive production, and the advantages and disadvantages of each.
• 3.5.3 — Distinguish production from productivity, explain the influences on each, and explain the effects of investment on productivity.
• 3.6.1 — Define total cost, average total cost, fixed cost, average fixed cost, variable cost and average variable cost.
• 3.6.2 — Calculate all six, and draw and interpret diagrams showing how a change in output affects costs.
• 3.6.3 — Define total revenue and average revenue.
• 3.6.4 — Calculate total revenue and average revenue, and explain the influence of sales on revenue.
• 3.6.5 — Explain the four objectives of firms: survival, social welfare, profit maximisation and growth.
• 3.7.1 — Describe the characteristics of a competitive market and its advantages and disadvantages, and state the effect of many firms on price, quality, choice and profit.
• 3.7.2 — Describe the characteristics of a monopoly market and its advantages and disadvantages, and state the effect of one firm on price, quality, choice and profit.

The table above is symmetrical for a reason: neither structure is better in every market. Competition delivers low prices where firms can reach an efficient scale individually — hairdressing, market trading, small manufacturing. A single regulated producer delivers lower prices where the scale economies are enormous and duplication is absurd — water pipes, rail track, an electricity grid. The deciding conditions are the size of the economies of scale, whether they are passed on, and whether the government regulates.

• If you got 3, 4 or 5 wrong, stop here. Those three are the whole of the labour-market and minimum-wage analysis in 3.3.2 — one of the three statements in this topic that carry an explicit instruction to draw and interpret diagrams. Ten minutes back in Topic 2 is the best-value revision available to you right now.
• Read the AO row across before you plan an answer. Paper 1 carries no AO3 at all, so a multiple-choice item never rewards evaluation — it rewards knowing the right chain. Evaluation is worth 15% of Paper 2, and it lives in the part (d) discussions of Section B.
• A developed analysis chain in this topic runs at least three links: change → direct effect in the market → further effect → effect on the decision-maker. Then name the condition that could change the outcome. Two links is description; three links plus a condition is analysis.
• 1. The central bank does not bank for the public It is banker to the government and banker to the commercial banks, and it is lender of last resort to banks. Households and firms bank with commercial banks. An answer that has a citizen opening an account at the central bank, or the central bank lending to a struggling household, has lost the distinction that 3.1.2 exists to test.
• 2. Economies of scale cut average cost, never total cost Total cost rises with output — producing more of anything costs more in total. What falls is the cost per unit. Write “average total cost falls as the scale of production increases” and the point is made; write “costs fall” and it is ambiguous at best.
• 3. A minimum wage below the equilibrium wage does nothing at all Employers are already paying more than the legal floor, so the floor never binds. Only a minimum wage set above the equilibrium changes the market, and then the surplus of labour is the horizontal gap Qs − Qd at that wage. Drawing the line below the intersection and then claiming unemployment is a contradiction on the page.
• 4. Demand for labour is derived Firms do not want workers for their own sake. They want them because consumers want the product. So the first link in almost every wage question is demand for the product, not the wage. If a question says demand for electric cars has risen, the labour-demand curve for car workers shifts right — the supply of workers has not changed.
• 5. Production and productivity are different measures Production is total output. Productivity is output per worker, or per unit of input. Hiring more workers raises production and may well lower productivity. The two move together only when the same workers produce more.
• 6. Fixed costs are not zero at zero output Rent, insurance and permanent salaries are paid whether the factory runs or not — that is what makes them fixed. It is variable cost that is zero at zero output. This is why a firm producing very little can be making a loss while still covering its variable costs.
• 7. Vertical means different stages, not different industries Same stage, same industry is horizontal. Different stages of the same production process is vertical — backward toward suppliers, forward toward customers. Unrelated industries is conglomerate. Three words, three meanings, and mixing up the first two is the standard error.
• 8. Average revenue equals price when every unit sells at the same price \(\text{AR} = \text{TR} \div Q = (P \times Q) \div Q = P\). It is not a separate quantity to be calculated from scratch, and it is not something different from the price. Stating that relationship is the whole of the explanation.
• 9. Do not draw a diagram for 3.7 Competitive markets and monopoly are examined in words and tables in this syllabus. The perfect-competition and monopoly cost-and-revenue diagrams belong to AS level, and reproducing one here answers a question the syllabus has not asked, while consuming minutes you needed for the analysis. State the effect on price, quality, choice and profit instead — those four are what the statement asks for.
• The one-line test for most of these. Before you write a sentence about cost, ask: per unit, or in total? Before you write a sentence about labour, ask: is this the wage moving, or the whole curve moving? Two questions, asked habitually, remove danger zones 2, 3, 4, 5 and 6.
• One sentence to carry into the examination. “The central bank is the bank for the government and for the banks; commercial banks are the banks for everyone else.” Write that and the two institutions will stay separate for the rest of the paper.
• The trap in row 5 A rise in productivity is read by many students as a supply-side change, because it is about workers. It is not. Productivity changes what a worker is worth to the employer, so it shifts the demand for labour. The supply curve answers a different question: how many people are willing and able to do this job at each wage. Nothing about the new tools changes that.
• Before you leave any labour-market diagram, check four things. Are both axes named with the variable and the labour being traded? Does the equilibrium dot sit exactly where the curves cross? Is the new curve parallel to the old one and labelled 2? Is the minimum-wage line above the equilibrium, with the surplus measured horizontally? Four checks, ten seconds, and they catch the errors that make an otherwise correct analysis contradict its own diagram.
• The word that decides the mark. Economies of scale lower average cost. Total cost still rises as output rises — making more of something costs more in total. Write “average total cost falls as the scale of production increases”, and never “costs fall”.
• The three errors these matrices exist to prevent “A vertical merger is two firms in the same industry.” So is a horizontal one. The deciding word is stage, not industry. “Economies of scale mean the firm's costs fall.” Total cost rises with output. It is average total cost that falls. “A bigger firm always has lower average cost.” Only up to the optimum output. Past the minimum of the U, growing further raises average cost — which is why an industry can contain efficient small firms and inefficient giants at the same time.
• “Fixed costs are zero when the factory is closed.” They are not, and that is exactly why they are called fixed. The rent falls due whether or not a single unit is made. It is the reason a firm may keep producing at a loss in the short run: if the price covers the variable cost of each unit and contributes something towards the rent, closing down immediately would leave it worse off.
• This is a short-run curve: the plant is fixed and the firm varies output within it. Figure 3.6 is the long-run curve, where the firm changes the scale of the plant itself. Both are U-shaped, and for different reasons — short run because of capacity, long run because of diseconomies of scale.
• Three arithmetic habits worth more than any formula. Use the original value as the denominator in every percentage change. Write the unit on every answer — $, $ per unit, units per worker, %. And check every ATC twice, once as TC ÷ Q and once as AFC + AVC: if the two disagree, the error is found before the examiner finds it.
• Supporting vocabulary — not a syllabus statement. The syllabus does not name normal or abnormal profit as terms you must define. They are used here only because 3.7.1 and 3.7.2 both require the effect on profit of many firms and of one firm, and these two words are the shortest accurate way to say what that effect is. Use them if they help, but nothing is lost by writing “profit above the minimum needed to keep the firm in the industry” instead — that phrase says the same thing and uses only terms the syllabus does name.
• Diagrams and the theory of perfect or imperfect competition are not required by this syllabus. Answer in words and tables.
• Diagrams are not required here either.
• Three things not to write about 3.7 Do not draw a diagram. Neither statement requires one, and the perfect-competition and monopoly cost-and-revenue diagrams are AS-level material. Do not write “monopolies always harm consumers”. A natural monopoly with large economies of scale and effective regulation can charge less than several small firms could. The judgement is conditional. Do not confuse “a monopoly” with “a big firm”. The defining feature is the absence of close competitors, protected by barriers to entry — not the firm's size in itself.
• Four more that show up in diagrams rather than in sentences The minimum wage drawn below the equilibrium, with unemployment claimed anyway. The diagram and the sentence then contradict each other, and one of the two has to be wrong. The surplus of labour measured vertically. It is the horizontal gap between the supply and demand curves at the minimum wage: Qs − Qd. Measuring it downwards from the old equilibrium gives the fall in employment, which is a different and smaller number. Total cost drawn starting at the origin, or converging on variable cost. TC starts at the level of FC on the vertical axis and runs exactly FC above VC at every output. If the gap changes, the diagram is claiming that fixed cost varies with output. Average fixed cost drawn touching the horizontal axis. AFC is a positive constant divided by output, so it approaches zero without ever reaching it. A curve that lands on the axis says the rent has vanished.
• One habit that fixes five of these at once. Before you write any sentence containing the word “cost”, decide whether you mean per unit or in total, and write the word. “Average total cost falls” and “total cost rises” are both true of the same firm at the same moment, and a sentence that says only “costs fall” does not tell the two apart.
• The totals below follow the published structure: Section A is one compulsory 20-mark question with parts (a) to (f), and each Section B question is worth 20 marks. The split of marks within a part, and the bracketed figures beside each answer point, are this chapter's own modelling of how a developed answer is built — they are not a Cambridge mark scheme, and no mark scheme is reproduced here.

• Only the published facts are stated here. This chapter does not predict questions, describe examiner behaviour or claim that any topic appears more often than another.
• All candidates take both papers, and all candidates are eligible for grades A* to G. There is no tiered entry in this syllabus, so no candidate is entered for a restricted set of papers or a restricted grade range. Exams are available in the June and November series, and in the March series in India.
• Across the whole qualification the weights are AO1 43%, AO2 47%, AO3 10%. Analysis is the largest single component, which is why every explanation in this chapter is written as a chain rather than as a list.
• Read the AO row across before you plan an answer. Paper 1 carries no AO3 at all, so a multiple-choice item never rewards evaluation — it rewards knowing the right chain. Evaluation is worth 15% of Paper 2, and it lives in the part (d) discussions of Section B.
• Official command words only. This syllabus uses analyse, calculate, define, describe, discuss, explain, give, identify and state. If a revision book sets you a question beginning “evaluate”, “assess” or “to what extent”, it is not written to the 2027–2029 syllabus. Part (d) of each 20-mark Section B question uses discuss.
• DEAL — for every discussion. Define the key term. Explain one side as a developed chain. Argue the other side just as fully. Land a judgement that names the condition deciding it — elasticity, the state of the economy, the time period, or how other decision-makers respond.