Multiple choice

With compound interest, a certain sum of money become 9 times in 36 years, In how many years it will become 243 times at the same rate of interest?

  1. 72

  2. 54

  3. 108

  4. 90

  5. None of these.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In compound interest, (1+r)^t = amount ratio. Given (1+r)^36 = 9. We need t for (1+r)^t = 243. Notice 9 = 3² and 243 = 3^5. So (1+r)^36 = 3² → 1+r = 3^(2/36) = 3^(1/18). For 243 = 3^5: (3^(1/18))^t = 3^5 → t/18 = 5 → t = 90 years. Option D is correct. Option A (72) assumes doubling pattern, which doesn't apply here.

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