Common Mistakes to Avoid

Part of Proportion · Section 14 of 16

Exam TipsUnit: NumberGCSE

This exam tips covers Common Mistakes to Avoid within Proportion for GCSE Mathematics. Revise Proportion in Number for GCSE Mathematics with 12 exam-style questions and 22 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 14 of 16 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.

Common Mistakes to Avoid

❌ Wrong: Confusing direct and inverse relationships ✅ Right: Check: if one increases, does other increase (direct) or decrease (inverse)?

Draw a mental graph - straight line (direct) or curve (inverse)?

❌ Wrong: Forgetting to find k first ✅ Right: Always find the constant before solving

Use the given values to find k, then substitute back

❌ Wrong: Using y = kx for inverse proportion ✅ Right: Inverse is y = k/x or xy = k

Check which formula fits the relationship type

❌ Wrong: Not checking answers make sense ✅ Right: Verify the direction of change is correct

If x doubles, should y double (direct) or halve (inverse)?

Practice questions for Proportion

y is directly proportional to x. Which equation could represent this relationship?

A. y = k/x
B. y = kx
C. y = k − x
D. y = x²

1 markfoundation

Explain how you can tell from a graph whether two quantities are in direct or inverse proportion.

2 marksstandard

Quick recall flashcards

Recipe Application

Recipe for 4 people uses 300g flour How much for 10 people? Flour ∝ People (direct) F = kP 300 = k × 4, so k = 75 For 10 people: F = 75 × 10 = 750g

Proportion Symbol

∝ means 'proportional to' Examples: y ∝ x (y is proportional to x) y ∝ 1/x (y is inversely proportional to x)

Real-World Applications

Exam Tips

12 questions on Proportion — practise free

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