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IAI Actuarial Core Principles · Business Economics

Production, Costs, Revenue and Profit in Price and Output Decisions

This chapter shows how a firm turns inputs into output, what that output costs, what it earns, and where profit is highest. You solve it by finding marginal cost (MC) and marginal revenue (MR), then choosing the output where MR = MC, provided MC is rising through MR.

What this chapter covers

This chapter follows a firm's decision from start to finish. The production function links inputs to output. Costs follow from the inputs and their prices. Revenue follows from the demand the firm faces. Profit is revenue minus cost, and the firm picks the output that makes it largest.

The four topics build on each other. Returns to scale and diminishing returns explain why cost curves are U-shaped. Cost curves and revenue curves then meet in the profit rule: MR = MC. You will use this rule again and again, so learn it well.

The chapter sits inside Microeconomics, which is the largest block in CB2 under the 2026 syllabus. It feeds directly into market structures such as perfect competition, monopoly and oligopoly, because each structure differs mainly in its revenue curve. It also supports macroeconomic ideas about supply and cost-push effects. In CB2, which opens with multiple-choice questions and then moves to written questions, this chapter gives you both quick recall items and calculation or diagram questions.

Microeconomics carries the largest share of the CB2 syllabus, and this chapter is its foundation. Market structure, pricing and competition questions all assume you know cost and revenue curves and the profit rule. Multiple-choice items test definitions and short calculations such as finding AC or MR from a table. Written questions ask you to draw diagrams, explain why a firm produces where it does, and say what happens in the short and long run. If you master this chapter, later microeconomics topics become much easier, so the effort pays back several times.

Production, costs, revenue and profit in price and output decisions: topics in the order to study them

  1. 1Production Function and Returns to ScaleStart here because every cost curve shape comes from how output responds to inputs.
  2. 2Types of Costs and Cost CurvesCosts come next because they translate the production function into money and give you MC and AC.
  3. 3Revenue Concepts: Total, Average and Marginal RevenueRevenue is the other half of profit, and you need MR before you can apply the profit rule.
  4. 4Profit Maximisation and Price-Output DecisionsStudy this last because it combines cost and revenue curves into the decision rule and the diagrams.

How to prepare Production, costs, revenue and profit in price and output decisions

Treat this as a chapter where each topic feeds the next. Spend your time on calculations and diagrams, not only on definitions.

  1. Read the production function topic and write down the difference between short run and long run, and between diminishing returns and returns to scale. Keep these in your own words.
  2. Build one cost table by hand with output, TC, FC, VC, AC, AVC and MC. Use simple numbers and check that MC = change in TC ÷ change in output.
  3. Sketch the cost curves from memory: AFC, AVC, ATC and MC. Mark where MC cuts AVC and ATC at their minimum points, and explain why.
  4. Do the same with revenue. Draw the demand, AR and MR curves for a price taker and for a firm facing a downward-sloping demand curve, and note how they differ.
  5. Practise the profit rule on tables and on simple equations. Find MR and MC, set them equal, check MC is rising, then compute price, total revenue, total cost and profit.
  6. Answer past-style written questions with a labelled diagram and a short explanation, covering profit, break-even and shutdown cases. State your assumptions.
  7. Finish with timed multiple-choice sets on definitions and quick calculations, and review every wrong answer.

Common mistakes in Production, costs, revenue and profit in price and output decisions

  • Mixing up diminishing returns with decreasing returns to scale

    Fix: Ask what is changing. One input only, others fixed: diminishing returns. All inputs together: returns to scale.

  • Including fixed cost when calculating marginal cost

    Fix: Use MC = change in TC ÷ change in Q. Fixed cost does not change with output, so it drops out.

  • Drawing MC crossing AC at the wrong point

    Fix: Remember that when MC is below the average, the average falls; when above, it rises. So MC must cut AC at its minimum.

  • Treating MR as equal to price for every firm

    Fix: Only price takers have MR = P. A firm facing a downward-sloping demand curve must cut price to sell more, so MR is below AR.

  • Applying MR = MC without checking the conditions

    Fix: Check that MC is rising through MR, then confirm price covers AVC in the short run before concluding the firm should produce.

  • Ignoring opportunity cost when discussing profit

    Fix: State that economic costs include the owner's opportunity cost, so zero economic profit means normal profit, not a loss.

Last-day revision: Production, costs, revenue and profit in price and output decisions

  • Short run: at least one input is fixed. Long run: all inputs can vary.
  • Diminishing returns concern one variable input with others fixed; returns to scale concern changing all inputs together.
  • Returns to scale: increasing if output rises by a greater proportion than inputs, constant if equal, decreasing if smaller.
  • TC = FC + VC; AC = TC ÷ Q; AVC = VC ÷ Q; AFC = FC ÷ Q.
  • MC = change in TC ÷ change in Q, and it is not affected by fixed cost.
  • MC cuts AVC and AC at their lowest points.
  • TR = P × Q; AR = TR ÷ Q, which equals price; MR = change in TR ÷ change in Q.
  • For a price taker, P = AR = MR and the demand curve is horizontal.
  • For a firm with a downward-sloping demand curve, MR lies below AR.
  • Profit is maximised where MR = MC and MC is rising through MR.
  • Economic profit = TR − TC, where TC includes opportunity cost, so normal profit is included in costs.
  • In the short run, a firm should keep producing if price covers AVC, and shut down if price is below AVC.

Production, costs, revenue and profit in price and output decisions practice questions

Production, costs, revenue and profit in price and output decisions in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Production, costs, revenue and profit in price and output decisions: frequently asked questions

What is the profit-maximising rule in CB2?

A firm maximises profit at the output where marginal revenue equals marginal cost, with marginal cost rising through marginal revenue. Then read the price from the demand curve and compare it with average cost to find profit per unit.

Why is the marginal cost curve U-shaped?

In the short run, MC first falls as extra workers use fixed equipment more fully. Then diminishing returns set in and each extra unit needs more input, so MC rises.

How is a price taker different from a firm with market power on revenue?

A price taker sells any quantity at the market price, so AR and MR are equal to price and the demand curve is horizontal. A firm with market power faces a downward-sloping demand curve, so MR is below AR.

When should a firm shut down in the short run?

A firm should shut down if price falls below average variable cost, because it cannot even cover the costs that change with output. If price is above AVC but below average total cost, it makes a loss but loses less by continuing to produce.

How should I practise this chapter for the exam?

Do calculations from tables first, then redraw the cost and revenue diagrams from memory with labels. Finish with timed multiple-choice sets and short written explanations of each decision.