6.5 Growth, decay and repeated percentage change — Practise with help
Try each question before opening a hint. Reveal the full working to check your method.
Warm-up: remember
- What multiplier models a 9% decrease?
- Work out 100 × 1.1².
Check your answers
- 0.91. 2. 121.
Practise with help
1. A quantity falls by 8%. Give its multiplier.
Hint
Find the percentage remaining.
Full working
100% − 8% = 92%, so multiplier 0.92.
2. Find 500 × 1.04³.
Hint
Use repeated multiplication or a calculator.
Full working
500 × 1.04³ = 562.432, about 562.43.
3. A £700 value decays by 15% yearly for two years.
Hint
Choose a multiplier and square it.
Full working
700 × 0.85² = £505.75.
Progress check: revisit your savings estimate. What calculation would make it exact?