Percentage change · Year 9
In Year 9 you learn: multipliers.
Prices, populations and pay change by percentages. A multiplier turns any percentage change into a single multiplication, and working backwards (a reverse percentage) finds the amount before the change.
Key facts
- Increase by r%: multiply by 1 + r/100 (up 15% → × 1.15).
- Decrease by r%: multiply by 1 − r/100 (down 15% → × 0.85).
- Successive changes: multiply the multipliers. Up 20% then down 20% is × 1.2 × 0.8 = × 0.96, a 4% decrease.
Worked examples
Example 1
Increase £240 by 15%.
Answer: £276
Example 2
A price rises by 25% and then falls by 20%. What is the overall change?
Answer: No overall change