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Problem #31 · August 27, 2026

Percentages

The city's population was 20 000 people. In the first year, the population increased by 5%5\%, and in the second year by a further 10%10\%. What was the city's population after two years?
  1. A21 000
  2. B22 050
  3. C23 000
  4. D24 200
  5. E23 100

WORKED EXAMPLE

Solution

Each year's increase is applied to the updated population from the previous year. After the first year: 20 000⋅1,05=21 00020\,000 \cdot 1{,}05 = 21\,000. After the second year: 21 000⋅1,1=23 10021\,000 \cdot 1{,}1 = 23\,100 people. Simply adding the percentages (15%15\%) and using the result is incorrect, because the second percentage is calculated from a larger base.
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