Some goods are linked. When one of them changes price, demand for the other shifts.
Substitutes: bought instead of each other
- A burger or a pizza slice
- Coffee or tea
- The bus or an electric scooter
Complements: bought together
- A burger and fries
- A printer and ink
- A phone and a phone case
The points to remember
- Substitute: a good bought instead of another, because it does a similar job.
- Complement: a good bought together with another, because they are used together.
Remember it as: Substitute = OR. Complement = AND.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Burgers are our good. Watch what happens to their demand when pizza (a substitute) or fries (a complement) change price.
Animated graph
Watch the graph build step by step in study mode.
The points to remember
- A substitute gets cheaper: demand for this good shifts left.
- A substitute gets more expensive: demand for this good shifts right.
- A complement gets cheaper: demand for this good shifts right.
- A complement gets more expensive: demand for this good shifts left.
Remember it as: Rival costs more: more for you. Partner costs more: less for you.
See how examiners mark answers
Answer exam-style questions with model answers. Learn exactly what earns marks and what doesn't.
Paper 1 asked this in May 2024, as part (a) for 10 marks.
Explain how a fall in the price of electric scooters might affect the price and output of their substitutes and of their complements.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Animated graph
Watch the graph build step by step in study mode.
What the diagrams must show
- Two diagrams: one for the substitute, one for the complement.
- Each with P and Q axes, S, D1 and D2.
- Substitute: D shifts left, so price and quantity both fall (P1 → P2, Q1 → Q2).
- Complement: D shifts right, so price and quantity both rise.
- In your writing, name each good and say which way its demand shifts.
How the 10 marks are given
| Marks | What your answer needs |
|---|---|
| 9–10 | Both parts fully explained, terms used correctly all the way through, the diagram included and fully explained |
| 7–8 | Both parts explained, terms mostly right, the diagram included and explained |
| 5–6 | Partly explained, some terms, the diagram included |
| 6 at most | Only one of the two parts answered, however good it is |