Question

A sum of money placed at C.I. doubles itself in 5 years. It will amount to eight times itself at the same rate of interest in

• A. 7 years
• B. 10 years
• C. 15 years
• D. 20 years

Answer 1

Answer: (C)

let sum=P
Time=2 Years
Amount=2P
According to the question
$\Rightarrow P{(1+\frac{r}{100})}^5=2P$
$\Rightarrow {(1+\frac{r}{100})}^5=2$
Cubic both side we gets
$\Rightarrow {(1+\frac{r}{100})}^{15}=8$
$\Rightarrow P{(1+\frac{r}{100})}^{15}=8P$
Hence,in 15 Years amount to eight times itself.