Question

A sum of money, lent out at simple interest, doubles itself in 8 years. Find:
(i) the rate of interest
(ii) in how many years will the sum become triple (three times) of itself at the same rate per cent?

Answer 1

Let P=Rs. 100 A=Rs. 200
I= Rs. 200 -Rs. 100 =Rs. 100, T= 8 years
$R=\frac{100\times I}{P\times T}=\frac{100\times 100}{100\times 8}=\frac{100}{8}=\frac{25}{2}$%
Now again P= Rs. 100
A=Rs. 300 I=Rs. 300-Rs. 100
=Rs. 200
$R=\frac{25}{2}$ %
$T=\frac{100\times I}{P\times R}=\frac{100\times 200}{100\times \frac{25}{2}}=\frac{100\times 200\times 2}{100\times 25}=16years$
So the given sum of money will become triple in 16 years.