• # question_answer Martin invested a certain sum of money at 10% p.a. simple interest for certain period of time. At the end of the period he got the amount equal to the five times the original amount. The period for which the amount has been invested by Martin is: A)  50 years                      B)  25 yearsC)  12 years                   D)  40 years

(d): Let time period be 't' years. $A=P\left( 1+\frac{rt}{100} \right)$ $\frac{A}{P}=5=\left( 1+\frac{rt}{100} \right)$ $5=\left( 1+\frac{10\times t}{100} \right)$ $\Rightarrow 4\times \frac{100}{10}=t$ $\Rightarrow t=40$