Question

A sum of money invested at $6$% p.a. simple interest for a certain period of time yields Rs. $960$ as interest. If this sum has been invested for $5$ years more, it would have yielded Rs. $2160$ as interest. Find the sum.

Answer 1

Let the sum be$Rs.x$

And we know $S.I.=\frac{PRT}{100}$

Then according to the question,

$\frac{x\times 6\times T}{100}=960$ ..............1

Also,$\frac{x\times 6\times (T+5)}{100}=2160$ ....................2

From eq. 1

$T=\frac{1600}{x}$

Putting this value in eq 2 we get,

$\frac{x\times 6\times (\frac{16000}{x}+5)}{100}=2160$

$\frac{16000+5x}{x}\times x\times 6=216000$

$96000+30x=216000$

$30x=120000$

$x=Rs.4000$

Hence sum $=Rs.4000$