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Proportion is a key topic in AQA GCSE Mathematics and describes how two quantities change in relation to each other. Understanding direct and inverse proportion allows you to solve problems ranging from simple recipes to complex scientific relationships. Higher-tier students must also be comfortable setting up and using algebraic equations for proportion.
Two quantities are in direct proportion if, when one increases, the other increases at the same rate. If one doubles, the other doubles. If one trebles, the other trebles.
| Property | Description |
|---|---|
| Relationship | As one quantity increases, the other increases at the same rate |
| Graph | A straight line through the origin |
| Equation | y = kx, where k is the constant of proportionality |
| Ratio | The ratio y/x is always constant |
| Notation | y is directly proportional to x is written as y is proportional to x |
The unitary method is the simplest approach at Foundation tier: find the value of one unit, then multiply.
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