IGCSE Maths / Ratios and percentages
Compound interest
Edexcel International GCSE Maths (4MA1), chapter 2: Ratios and percentages, specification point 1.6b. Part of the full course.
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Compound interest is calculated on the amount you have at the start of each year, so the amount grows by the same multiplier each year. Use a power for the number of years, and distinguish the final total from the interest earned.