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0580/43 Oct/Nov 2025, Question 15: Compound Interest

Cambridge IGCSE Mathematics 0580 · Paper 43 (Extended) · Calculator · 5 marks

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The question, in short

Town population 54 000 falls exponentially at 2% per year; find the 4-year decrease and the number of complete years until it first drops under 44 000.

Summarised in our own words. Use the official paper for the exact wording and any diagrams.

Part (a) · 3 marks

Calculate how much the population of 54 000 decreases over 4 years at 2% exponential decay per year.

  1. 1Population after 4 years = 54 000 × 0.98⁴
  2. 2= 49 807.9
  3. 3Decrease = 54 000 − 49 807.9 = 4192

Answer4192 or 4193

Part (b) · 2 marks

Find how many complete years are needed for the population starting at 54 000 to first fall below 44 000.

  1. 154 000 × 0.98¹⁰ = 44 122 (not below 44 000)
  2. 254 000 × 0.98¹¹ = 43 240 (below 44 000)
  3. 311 years

Answer11

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