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CA Foundation · Quantitative Aptitude · Sequence and Series

A town's population grows by a constant 20% every year, forming a geometric progression. If the population at the start of the first year is 50,000, what will it be at the start of the fourth year?

The population is 86,400. The start of the fourth year is three years of growth after the start of the first year, so the population is 50,000 multiplied by 1.2 cubed, which is 1.728, giving 86,400.

  1. A80,000
  2. B86,400Correct
  3. C72,000
  4. D1,03,680

Explanation

Start of year 4 is after 3 years of growth: 50,000 × (1.2)^3 = 50,000 × 1.728 = 86,400. The option 1,03,680 uses 4 growth periods (50,000 × 1.2^4 = 1,03,680), which is the mistake of counting the wrong number of terms.

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