This exam tips covers Common Mistakes to Avoid 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 8 of 9 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Common Mistakes to Avoid
X Confusing direct and inverse proportion
Direct: both go up together. Inverse: one up, one down.
Check: does doubling x DOUBLE y or HALVE y?
X Forgetting the graph passes through (0,0)
Direct proportion ALWAYS passes through origin
If x = 0, then y = k × 0 = 0
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 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.
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.