A sum of money triples itself in 3 years at simple interest. In how many years will it become 9 times of itself?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 12 years
Simple interest grows by the same amount every year, so the time needed is in proportion to the interest needed.
Tripling: amount \(3P\), so the interest is \(2P\) in 3 years.
Nine times: amount \(9P\), so the interest needed is \(8P\), four times as much.
Time \(=4\times3=12\) years
Tip: With simple interest, a sum becomes 9 times in 4 times the period it takes to become 3 times, not in twice the period; doubling the time works only for compound interest.