Question : A sum of money placed at compound interest doubles itself in 5 years. In how many years would it amount to eight times itself at the same rate of interest?
Option 1: 10 years
Option 2: 15 years
Option 3: 7 years
Option 4: 20 years
Correct Answer: 15 years
Solution :
By applying the formula: Amount = P[
Let the sum be
Amount =
⇒
⇒
Now, the sum becomes 8 times after
⇒
⇒
Thus,
Hence, the correct answer is 15 years.