If a sum of money placed at compound interest becomes 3 times of itself in 3 years. In how many years will it be 9 times at the same rate of interest?
Correct Answer: 6 years
Explanation:
Let the principle be P then amount be 3P
∵ 3P =P(1 + r/100)3
⇒ 3 = (1 + r/100)3
On squaring on both the sides,
⇒ (3)2 = {(1 + r/100)3}2
∴ 9 = (1 + r/100)6
Hence,it will become 9 times in 6 years.
