Question

The si of ` 600 for 4 yr and that of ` 600 for 2 yr together is ` 180. what is the rate of interest per annum?

Answer 1

Answer: The rate of interest is 5%.

We arrive at the answer as follows:

The formula for Simple interest (SI) is :

$SI = P * n* r$

where

P is Principal invested

n is number of years

r is interest rate

In this question, P is 600 in both cases, n is 4 for the first case and 2 for the second case.

The interest on both these amount is 180.

We can write this mathematically as :

$180 = (600*4*r) + (600*2*r)$

$180 = 2400r + 1200r$

$180 =3600r$

$r =\frac{180}{3600}$

r = 0.05 or 5%.