Question

17. At what rate per cent per annum will 1640 amount
to 1968 in 2whole 1/2 years​

Answer 1

Given :-

Principal = ₹1640

Interest = ₹1968

Time = 5/2 years

To Find :-

The Rate of Interest.

Solution :-

We know that,

$I\: =\: {\sf{\dfrac{P\: \times\: R\: \times\: T}{100}}}$

On inserting the values in the formula

We get ,

$I\: =\: {\sf{\dfrac{164\: \times\: R\: \times\: 5}{100\: \times\: 2}}}$

${\sf{\implies\: I\: =\: 41R}}$

Also,

A = P + I

But also given that, A = ₹1968

Now,

${\sf{\implies\: 1968\: =\: 1640\: +\: 41R}}$

${\sf{\implies\: 1968\: -\: 1640\: =\: 41R}}$

${\sf{\implies\: 41R\: = 328}}$

${\sf{\implies\:R\: =\: {\dfrac{328}{41}}}}$

${\sf{\implies\:R\: =\: 8}}$

Therefore, rate of interest is 8%