Worked Example 1: Population Growth

Part of Compound Interest · Section 4 of 6

Study NotesUnit: Ratio & ProportionGCSE

A colony of 500 bacteria grows by 20% each hour. How many after 5 hours?

Step 1 Identify type and multiplier

Growth, so multiplier = 1 + 0.20 = 1.2

Step 2 Write formula

y = 500 × 1.2⁵

Step 3 Calculate

y = 500 × 2.48832 = 1244 bacteria (to nearest whole)

This study notes covers Worked Example 1: Population Growth within Compound Interest for GCSE Mathematics. Revise Compound Interest in Ratio & Proportion for GCSE Mathematics with 12 exam-style questions and 4 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 6 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.

Practice questions for Compound Interest

Which formula correctly calculates the amount A after compound interest at rate r% per year for n years on principal P?

A. A = P × (1 + r/100) × n
B. A = P × (1 + r/100)^n
C. A = P + P × r/100 × n
D. A = P × r^n / 100

1 markfoundation

£2,000 is invested for 4 years. - Account A pays 5% simple interest per year. - Account B pays 4.5% compound interest per year. Which account gives more money after 4 years? Show all working.

3 marksstandard

Quick recall flashcards

Exponential Decay

N = N₀ × (1 - r)^t for decay rate r

Growth vs Decay

Growth: multiply by (1+r). Decay: multiply by (1-r). The multiplier is raised to the power of n (time periods).

Method: Exponential Problems

Worked Example 2: Depreciation

12 questions on Compound Interest: practise free

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