Multiple choice

A sum triples itself in three years at simple interest. In how many years will the same sum become nine times itself at the same rate?

  1. 18

  2. 9

  3. 12

  4. 27
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In simple interest, if a sum triples in 3 years, the interest earned is 2 times the principal in 3 years. To become 9 times, the interest must be 8 times the principal. Since 2 times the principal takes 3 years, 8 times the principal takes 3 * (8/2) = 12 years.

AI explanation

If a sum triples in three years under simple interest, the interest earned is twice the principal. Let the principal be P, so the interest is 2P over three years, giving a yearly interest of 2P/3. To become nine times itself, the required interest is 8P, which takes 8P divided by (2P/3) years. This equals 12 years.

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