Multiple choice

A sum of money invested at compound interest doubles itself in 5 years. In how many years will it become 8 times its initial value at the same interest rate?

  1. 10 years

  2. 15 years

  3. 20 years

  4. 25 years

  5. 12 years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Compound interest doubling in 5 years means A = P(1+r)^5 = 2P. We want 8P = P(1+r)^n. Since 8 = 2^3, we need (1+r)^n = (2^3) = ((1+r)^5)^3 = (1+r)^15. So n = 15 years.

AI explanation

Because compound interest grows exponentially, multiplying the initial sum by 2 three times (2 times 2 times 2 = 8) means the original sum must double during three separate intervals. Since the money takes 5 years to double one time, it will take 5 times 3 = 15 years to become eight times its initial value.

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