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 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: 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)
Practice questions for Percentages
Which calculation correctly finds 35% of £240 using the decimal method?
Which formula correctly expresses one quantity as a percentage of another?
Quick recall flashcards
Percentage to decimal
Divide by 100
75% = 0.75
8% = 0.08
150% = 1.5
Move decimal point 2 places left
What is a percentage?
Parts per hundred
Percent = per cent = per 100
% symbol means 'out of 100'
50% = 50/100 = half