Multiple choice

A sum of money placed at compund interest triples itself in 5 years. In what time will it amount to nine times itself ?

  1. 10 years

  2. 15 years

  3. 20 years

  4. 18 years

  5. None of these
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A Correct answer
Explanation

If money triples in 5 years at compound interest, the growth factor is 3^(1/5) per 5-year period. To reach 9 times (3^2), we need 2 periods of 5 years each, so 10 years. The pattern: 3 times in 5 years, 9 times in 10 years, 27 times in 15 years. This follows from (3)^(t/5) = 9, solving for t.

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