0 vote
A sum of money placed at compound interest double itself in 3 years. In how many years will it amount to eight times itself?
Asked on by Guest | Votes 0 | Views: 622 | Tags: interest | simple interest | quantitative aptitude | Add Bounty
A sum of money placed at compound interest double itself in 3 years. In how many years will it amount to eight times itself?
1). 12 years
2). 13 years
3). 9 years
4). 16 years
1 answers
1 vote
⇒ Let, Principal be Rs. x then Amount = Rs. 2x, Rate = r% and Time (n) = 3 years.
⇒ A = P × [1 + (r/100)]n
⇒ 2x = x × [1 + (r/100)] 3
⇒ 2 = [1 + (r/100)] 3 ------ 1
⇒ If sum become 8 times in the time n years then,
⇒ 8 = [1 + (r/100)] n
⇒ 23 = [1 + (r/100)] n
⇒ putting the value of equation 1 into above we get,
⇒ ([1 + (r/100)] 3)3 = [1 + (r/100)] n
∴ n = 9