This module covers how sellers respond to price, where a market settles, and how to explain what happens when conditions change. It is the second half of the market model that starts in demand relationships, and it feeds directly into elasticity and market failure concepts.
What is in this module, and why does it matter?
In IGCSE Economics (0455), almost every later topic is explained by returning to a supply and demand diagram. If the supply side is shaky, the explanations for prices, wages, exchange rates and government measures all become harder. The skills here are small but they are used again and again: separate a movement from a shift, find equilibrium, describe a shortage or surplus, and state the assumptions you rely on.
Check the current Cambridge Economics syllabus page for the exact wording of what is assessed in your examination year.
What should you know before starting?
You should be comfortable reading a price and quantity table, plotting two lines on one set of axes and using the word “demand” correctly. If you are not, spend a short session on demand relationships first. Basic percentage change is also helpful, and the percentage-base explorer lets you practise it on made-up numbers.
An orienting example
Port Merah is a fictional town where sellers offer reusable lunch boxes. This schedule is used through the module.
| Price (RM) | Quantity demanded | Quantity supplied |
|---|---|---|
| 10 | 90 | 20 |
| 15 | 75 | 40 |
| 20 | 60 | 60 |
| 25 | 45 | 80 |
| 30 | 30 | 100 |
At RM20 buyers want 60 and sellers offer 60, so RM20 and 60 boxes is the equilibrium. At RM15 buyers want 75 but sellers offer 40, a shortage of 35. At RM25 sellers offer 80 but buyers want 45, a surplus of 35.
Now suppose the price of plastic rises. Sellers now offer 14 fewer boxes at every price, a leftward shift of supply and not a move along the old curve. The new equilibrium is RM22 and 54 boxes.
The whole module is about telling these two kinds of change apart and explaining each one clearly.
In what order should you study the lessons?
- Distinguish a supply shift from a price response: start here, because every later lesson depends on knowing which kind of change you are describing.
- Find an equilibrium from supplied schedules: reading two columns side by side and locating the price where they match.
- Explain a shortage with a price adjustment model: turning a gap on the table into a written sequence of events.
- Trace simultaneous shifts without false certainty: what to say when two things change at once and the answer is only partly determined.
- State an assumption behind the model: the sentence that turns a memorised paragraph into an evaluation.
Then work through the supply and equilibrium practice set.
What are the common traps?
- Writing “supply increases” when the price rose and sellers simply offered more. That is a rise in quantity supplied.
- Saying a shortage means supply has fallen. A shortage is a gap at one price, and the curves have not moved.
- Claiming both price and quantity will definitely change in a stated direction when two curves shift together.
- Drawing a correct diagram and writing no sentences that connect it to the question.
- Using real-world examples with political opinions. Keep to facts and the model.
How should you use the practice set?
Attempt the questions without looking at the answers, then open each worked answer and compare your reasoning, not just your final number. Note which lesson the practice page points you to for each type of error. The mistake log and retest queue is a simple way to keep track of repeated slips.
Many students can follow each lesson but still lose marks when the question changes its wording. That is where online one-to-one Economics tuition can help: a teacher can ask the follow-up questions an examiner would, and see where your reasoning breaks.