Difficulty: Intermediate | Prerequisites: Basic supply and demand, market structures overview
Consumer theory explains how people decide what to buy given limited income, and production cost theory explains how firms turn inputs into outputs at various costs. These two sides of the market, demand and supply, form the analytical core of intermediate microeconomics. You should already understand basic supply and demand and the idea of market structures before tackling this material. If utility or marginal analysis are unfamiliar terms, this is the right place to start.
Consumers maximise utility by choosing the bundle on the highest indifference curve they can afford given their budget constraint. Firms face costs that vary with output: marginal cost, average total cost and their relationship drive pricing and output decisions. Technological change (including process improvements, not just new machines) shifts cost curves and is a key driver of long-run competitiveness.
Utility
The enjoyment or satisfaction a person receives from consuming goods and services. Utility is not directly measurable in practice.
Marginal utility
The change in satisfaction from consuming one additional unit of a good. In simple terms, how much happier the next unit makes you.
Indifference curve
A curve showing all combinations of two goods that give a consumer the same level of satisfaction. The consumer is equally happy at any point along the curve.
Budget constraint
The line showing all combinations of two goods a consumer can afford given their income and the prices of the goods. Consumption bundles are affordable if they are along or inside the budget constraint line.
Marginal rate of substitution (MRS)
The rate at which a consumer is willing to trade one good for another while maintaining the same level of satisfaction. It is the slope of the indifference curve at any given point.
Marginal cost (MC)
The additional cost of producing one more unit of output. Calculated as the change in total cost divided by the change in quantity.
Marginal product of labour
The additional output produced by hiring one more worker, holding other inputs constant.
Technological change
A positive change in a firm's ability to produce, including improvements in products or production processes. This covers new equipment, better factory layouts, worker training and replacing workers with automation. All of these count, not just the introduction of new machines.
Economies of scale
Cost advantages that arise when a firm increases its scale of production, causing average cost to fall. In simple terms, making more of something gets cheaper per unit.
Utility is the satisfaction from consuming goods and services. It is not directly measurable.
To maximise utility, a consumer chooses the consumption bundle on the highest indifference curve that is still on or inside the budget constraint.
At the optimal bundle, the marginal rate of substitution (slope of the indifference curve) equals the price ratio (slope of the budget constraint).
When deciding between consuming now and saving, consumers should allocate spending and saving so that the marginal utility per pound (or dollar) is equal across all uses.
Indifference curves do not intersect one another. If they did, it would create a logical contradiction about preferences.
Consumption bundles are affordable if they are along or inside the budget constraint line. Bundles outside the line are unaffordable.
If prices remain the same, an increase in income shifts the budget constraint outward (parallel shift), expanding the set of affordable bundles.
A consumer deciding how much to spend on transportation versus other goods will choose the combination that makes them as well off as possible within their budget.
Marginal cost is the change in total cost divided by the change in quantity.
Example from the source material: a pizza shop has total cost of $800 with zero workers and zero pizzas. Adding one worker produces 200 pizzas at a total cost of $1,450. The marginal cost of the 200th pizza is calculated as ($1,450 minus $800) divided by 200, which equals $3.25.
When marginal cost is below average total cost, average total cost is falling. When marginal cost is above average total cost, average total cost is rising.
The marginal cost curve intersects the average total cost curve at its minimum point.
Technological change includes any improvement in products or production processes.
Examples that count: installing new equipment, redesigning store layouts, rearranging a factory floor to increase production, worker training, replacing workers with robots. All of these are technological change.
Starbucks installing new espresso machines and redesigning store layouts both count as technological change because both improve the production process.
Walmart matches prices from large online sites but not from local retailers or its own brick-and-mortar stores.
Walmart matches online prices because it faces more competition from large online sites than from local retailers.
Walmart does not match its store prices to competitors because it believes customers will continue buying in stores even if competitors lower prices. The convenience of in-store shopping gives Walmart some market power in its physical locations.
Students often think utility is measurable in some objective unit. It is not. Utility is ordinal (we can rank preferences) but not cardinal in any practical sense.
Students sometimes place the optimal consumption bundle where indifference curves cross. Indifference curves never intersect, and the optimal bundle is on the highest indifference curve that touches the budget constraint.
Students confuse marginal cost with average cost. Marginal cost is the cost of one more unit; average cost is total cost divided by total quantity. They are related but different.
Students sometimes think technological change requires inventing something new. It does not. Rearranging a factory floor, training workers or redesigning a store layout all qualify as technological change.
The utility maximisation rule (highest indifference curve on the budget constraint) is tested in nearly every exam. Know it precisely.
Expect a question about what happens to the budget constraint when income rises with prices held constant (it shifts outward).
The marginal cost calculation from a production table (change in total cost divided by change in quantity) is a staple of problem sets and exams. Work through the pizza example until the arithmetic is automatic.
Technological change questions often test whether students understand that process improvements (not just new inventions) count. The Starbucks example is typical.
The MC/ATC relationship (MC below ATC pulls ATC down, MC above ATC pulls ATC up) appears in every market structure analysis.
True or false: Utility can be measured precisely in standard units. (False. Utility is ordinal, not cardinally measurable.)
Fill in the blank: Consumption bundles are affordable if they are along or ______ the budget constraint line. (Inside.)
True or false: Rearranging a factory floor to increase production counts as technological change. (True.)
Fill in the blank: When marginal cost is below average total cost, average total cost is ______. (Decreasing.)
True or false: An increase in income, with prices unchanged, shifts the budget constraint inward. (False. It shifts outward.)
Q: To maximise utility, where does a consumer choose their consumption bundle?
A: On the highest indifference curve that is still on or inside (tangent to) the budget constraint.
Q: A pizza shop has zero pizzas at a total cost of $800 and 200 pizzas at a total cost of $1,450. What is the marginal cost of the 200th pizza?
A: ($1,450 minus $800) / 200 = $650 / 200 = $3.25.
Q: Starbucks will install new espresso machines and redesign store layouts. Are these examples of technological change?
A: Yes, both. Technological change includes improvements in products or production processes, not only new inventions.
Q: If prices remain unchanged and income increases, what happens to the budget constraint?
A: It shifts outward (a parallel shift), expanding the set of affordable consumption bundles.
Q: When deciding between consuming now and saving, how should consumers allocate their income?
A: So that the marginal utility per dollar (or pound) is equal between spending and saving. This ensures no reallocation could increase total satisfaction.
Utility maximisation and budget constraints underpin demand theory, which feeds into every market structure analysis. The cost concepts here (marginal cost, average total cost, their relationship) reappear in the monopoly, monopolistic competition and oligopoly material. Technological change connects to long-run cost curves and to why firms in monopolistic competition can sometimes sustain profits by improving their products.
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