❌ Wrong Multiplier
Mistake: 20% growth → multiply by 0.2
Correct: 20% growth → multiply by 1.2
Remember: Growth = 1 + rate, Decay = 1 - rate
❌ Linear Thinking
Mistake: "5% growth for 4 years = 20% total growth"
Correct: (1.05)⁴ = 1.216 = 21.6% total growth
Remember: Compound effects are not linear
❌ Time Period Confusion
Mistake: Monthly rate for 2 years = n = 2
Correct: Monthly rate for 2 years = n = 24
Remember: Match periods to the rate
❌ Half-life Miscounting
Mistake: Half-life = 3 years, total time = 9 years → n = 3
Correct: 9 ÷ 3 = 3 periods → n = 3 ✓
Remember: Divide total time by half-life period
This diagram covers Common Mistakes to Avoid within Growth & Decay for GCSE Mathematics. Revise Growth & Decay in Number for GCSE Mathematics with 12 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 8 of 9 in this topic. Focus on the labels, the relationships between parts, and the explanation that turns the diagram into an exam-ready answer.
Practice questions for Growth & Decay
A quantity increases by 8% each year. Which multiplier should be used for each year?
Explain the difference between simple interest and compound interest.