Question

A sum of money double itself in 4 years at compound interest. In how many years it will become eight times at same rate of interest

• A. 12 years
• B. 18 years
• C. 24 years
• D. 16 years

Answer 1

Answer: (A)

12 years

$A=P{(1+\frac{R}{100})}^T$
$2x=x{(1+\frac{R}{100})}^4$
$(1+\frac{R}{100})=2^{1/4}$
$8x=x{(1+\frac{R}{100})}^T$
$\because 1+\frac{R}{100}=2^{1/4}$
$\therefore 8=2^{T/4}$
$2^3=2^{T/4}$
$\frac{T}{4}=3$
$T=12years$