Multiple choice

A certain sum of money lent out at a certain rate of interest per annum, doubles itself in 10 years. In how many years will it treble itself?

  1. 20 years

  2. 16 years

  3. 12 years

  4. 10 years
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Simple interest formula: A = P(1 + rt/100). If it doubles, A = 2P, so 2P = P(1 + r*10/100) => 1 = 10r/100 => r = 10%. To treble, A = 3P, so 3P = P(1 + 10*t/100) => 2 = 10t/100 => t = 20 years.

AI explanation

For the sum to double in 10 years under simple interest, the interest earned equals the principal, meaning the interest for 10 years is 1 part principal. To treble itself, the interest must equal 2 parts principal, which takes exactly twice as long at the same simple interest rate. Therefore, it will take 10 x 2 = 20 years.

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