Multiple choice

A sum of money doubles itself in 7 years at simple interest. In how many years it will become 4 times?

  1. 14

  2. 21

  3. 16

  4. 24

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If a sum doubles in 7 years at simple interest, it means the interest earned in 7 years equals the principal. To become 4 times, we need interest equal to 3 times the principal. Since 7 years gives 1×principal as interest, we need 3 × 7 = 21 years to get 3×principal as interest. At 21 years, total amount = principal + 3×principal = 4×principal.

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