Question

A certain sum is invested for a certain time. It amounts to Rs. $600$ at $10$ % per annum. But when invested at $5$% per annum, it amounts to Rs. $400$. Find the time.

Answer 1

Lat the certain sum be $S$ and time be $t$ years

According to question

$S+S\times 10\times t=600$ .....(1)

$S+S\times 5\times t=400$ .....(2)

From (1)

$S=\frac{600}{(1+10t)}$.....(3)

From (2)

$S(1+5t)=400$

$\frac{600}{(1+10t)}(1+5t)=400$

Solving we get $t=0.2$ years