A certain sum was invested at a certain rate of simple interest. It took 20 years to quadruple. Find the time that the sum would take to become 9 times, if the rate of interest was 5 percentage points more (in years).

Options

A. 30
B. 36
C. 40
D. 45

Answer

C

Explanation

Let the sum be Rs. P it amounted to Rs. 4P in 20 years . S.I. for 20 years =3P.
Let the rate of interest be R% per annum
`3P=((P)(20)(R ))/(100)`
R=15
If the sum becomes 9 times,
S.I. =Rs. 8P.
Let the required time be t years.
`8P=(P(t)(15+5))/(100) therefore t=40`