This introduction covers What Is Direct Proportion? within Proportion Graphs for GCSE Mathematics. Revise Proportion Graphs in Ratio & Proportion for GCSE Mathematics with 14 exam-style questions and 4 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 1 of 6 in this topic. Use this introduction to connect the idea to the wider topic before moving on to questions and flashcards.
What Is Direct Proportion?
If you buy 2 pizzas for £10, 4 pizzas cost £20, and 6 pizzas cost £30. Double the pizzas = double the price. This is direct proportion! When one quantity doubles, the other doubles too. The ratio between them stays CONSTANT.
Practice questions for Proportion Graphs
Which of the following describes the graph of a direct proportion relationship?
Aisha says: 'Because the graph of y against x is a straight line, y must be directly proportional to x.' Is Aisha correct? Explain your answer.
Quick recall flashcards
Finding k
Use given values to find constant k, then apply to new values
Direct vs Inverse
Direct: both increase together (y ∝ x). Inverse: one increases, other decreases (y ∝ 1/x).