This exam tips covers Common Mistakes to Avoid within Percentages for GCSE Mathematics. Revise Percentages in Number for GCSE Mathematics with 14 exam-style questions and 22 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 14 of 15 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 14 of 15
Practice
14 questions
Recall
22 flashcards
Common Mistakes to Avoid
❌ Wrong: 30% of 80 = 30 × 80 = 2400
✅ Right: 30% of 80 = 0.3 × 80 = 24
Convert percentage to decimal first
❌ Wrong: 20% increase = × 0.2
✅ Right: 20% increase = × 1.2
Add to 100% for increase (120% = 1.2)
❌ Wrong: 15% decrease = × 1.15
✅ Right: 15% decrease = × 0.85
Subtract from 100% for decrease (85% = 0.85)