This introduction covers What is Direct Proportion? within Direct Proportion for GCSE Mathematics. Revise Direct Proportion in Ratio & Proportion for GCSE Mathematics with 15 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 1 of 9 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 1 chocolate bar for £1, then 2 bars cost £2, 3 bars cost £3, and so on. The cost goes up at the SAME RATE as the number of bars - they're in direct proportion. When one quantity doubles, the other doubles too. The ratio between them stays constant!
Visual Guide
Practice questions for Direct Proportion
Which of the following correctly reads the mathematical statement y ∝ x?
Explain what it means for y to be directly proportional to x. Your answer should refer to the equation and the graph.
Quick recall flashcards
What does the symbol ∝ mean?
'is proportional to'
y ∝ x means 'y is proportional to x'
This is equivalent to writing y = kx for some constant k.
What does the graph of y = kx look like?
A straight line passing through the origin (0, 0).
The gradient of the line equals k.
If the line does NOT pass through (0,0), it is NOT direct proportion.