Multiple choice

A sum of money doubles itself in 10 years at simple interest. In how many years would it become 5 times of itself?

  1. 30

  2. 45

  3. 40

  4. 50
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Simple interest: A = P(1 + rt). Doubles in 10 years: 2P = P(1 + 10r) => 1 = 10r => r = 0.1 (10%). To become 5 times: 5P = P(1 + rt) => 4 = rt => 4 = 0.1t => t = 40 years.

AI explanation

Using the simple interest formula, if a sum doubles in 10 years, the interest earned equals the principal, so P = (P times R times 10)/100, which means the rate of interest is 10%. To make the sum five times itself, the interest must be four times the principal, giving 4P = (P times 10 times T)/100. Solving for T yields a time period of 40 years.

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