Question

If the interest on $₹2,400$ be more than the interest on $₹2,000$ by $₹60$ in $3\text{years}$ at the same rate per cent; find the rate.

Answer 1

Calculate interest for the principal of $Rs.2400$

Let the rate of interest be $R$

Given:

Principal $\left(p\right)=Rs.2400$

Time $\left(T\right)=3\text{years}$

Using the simple interest formula we get,

Simple interest $\left(SI\right)=\frac{2400\times R\times 3}{100}$

$=24\times R\times 3$

Simple interest $\left(SI\right)=72R$


Calculate interest for the principal of $Rs.2000$

We have:

Principal $\left(P\right)=Rs.2000$

Time $\left(T\right)=3\text{years}$

Using the simple interest formula we get,

Simple interest $\left(SI\right)=\frac{P\times R\times T}{100}$

$=\frac{2000\times R\times 3}{100}$

$=20\times R\times 3$

Simple interest $\left(SI\right)=60R$

Calculate rate of interest

According to the question,

$72R-60R=60$

$12R=60$

$R=\frac{60}{12}=5\%$

Hence, the required rate of interest is $5\%$.