Elasticity measures how strongly quantity responds when something else changes, usually price or income. It sits between the demand and supply topics and the later work on market failure, so it is worth learning carefully.
Check the Cambridge subject page for your exam year to see which measures are listed.
Why does elasticity matter in the syllabus?
It turns the shape of demand and supply into numbers you can interpret. Questions ask you to calculate a value, explain what it shows, link it to revenue and judge how far the conclusion holds. Marks go to the working, the meaning and the stated assumptions.
What should you know first?
You need percentages, ratios and the ideas in demand relationships and supply and equilibrium. If percentages are shaky, the first lesson fixes that.
Orienting example
Kopi Sudut, a fictional café, raises the price of iced coffee from RM4.00 to RM4.60. Weekly sales fall from 200 cups to 170 cups.
Price change = 0.60 ÷ 4.00 × 100 = +15%. Quantity change = −30 ÷ 200 × 100 = −15%. PED = −15 ÷ 15 = −1, so demand is unitary elastic over this range.
Revenue before = 4.00 × 200 = RM800. After = 4.60 × 170 = RM782. It dips slightly, because unitary demand leaves revenue roughly unchanged, not exactly. The result also assumes nothing else changed.
What order should you study the lessons in?
- Calculate percentage changes using the specified base: every later step depends on getting the base right.
- Interpret an elasticity value and sign: turns a number into a statement about responsiveness.
- Connect price elasticity with a revenue change: the most common application in exam questions.
- Explain why a short-run response may differ: adds time as a reason in written answers.
- Avoid comparing elasticities from incompatible methods: teaches you to judge when two values belong together.
Common traps
- Dividing by the new value instead of the old value.
- Reading −1.5 as smaller than −0.2 because of the sign.
- Saying “elastic means revenue rises”, without stating the direction of the price change.
- Giving “more time” as the reason for a long-run response, with no named adjustment.
- Comparing values from different methods or periods.
How should you use the practice set?
Do the lessons first, then attempt the elasticity practice set on paper. Use the percentage-base explorer and the elasticity tutor to check working, and record repeated errors in the mistake log.
Individual feedback on written explanations can save time before an exam. That is part of our online one-to-one Economics tuition.