Multiple choice

A sum borrowed under compound interest doubles itself in 10 years. When will it become four fold of itself at the same rate of interest?

  1. 15 years

  2. 20 years

  3. 24 years

  4. 40 years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If an amount doubles in 10 years under compound interest, it will become fourfold (2×2) in 20 years. This is because compound interest grows exponentially - doubling once takes 10 years, and doubling again (to reach 4x) takes another 10 years. The formula A = P(1 + r)^t shows that the time to multiply by a factor n follows logarithmic growth.

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