Question

A sum when reckoned at 7$\frac{1}{2}\%$ per annum amounts to Rs. 3920 in 3 years. Find the sum

Answer 1

As we know that, simple interest (s.i.) $=\frac{p\times r\times t}{100}$

Where p = principal
r = rate of interest per annum
t= time in years

In this case,
Amount (A)$=3920,r=7.5\%,t=3$
Amount (A) = p + s.i.

$\Rightarrow 3920=p+\frac{p\times r\times t}{100}$
$\Rightarrow 3920=p+\frac{p\times 7.5\times 3}{100}$
$\Rightarrow 3920=p(1+\frac{22.5}{100})$
$\Rightarrow 3920=p(1+0.225)$
$\Rightarrow p=\frac{3920}{1.225}$
$\therefore p=Rs.3200$