Multiple choice

If a certain sum on compound interest becomesfour times in 5 years, then in what time period, at thesame interest rate, will the sum become 64 times?

  1. 10 years

  2. 15 years

  3. 20 years

  4. 25 years

  5. 80 years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In compound interest, if it becomes 4 times in 5 years, it becomes 4^n times in 5n years. 64 = 4^3. So time = 5 * 3 = 15 years.

AI explanation

When a sum becomes four times in 5 years, it means it doubles twice in 5 years, making the doubling time 2.5 years. To become 64 times, the sum must double six times. Multiplying the six required doublings by the 2.5 years it takes for each doubling gives a total period of 15 years.

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