Question

On simple interest, a certain sum
becomes 97,920 in 3 years, and in
5 years it becomes * 1,15,200. Find
the rate of intorest?
(a) 10%
(b) 11.2%
(c) 12%
(d) 13.6%​

Answer 1

Answer:

12%. IND.

Step-by-step explanation:

A - P = s.i

97,920 - p = 3pr/100

97920 × 100 = p(3r + 100) ..(1)

similarly,

1,15,200 × 100 = p(5r + 100) ..(2)

on deviding (2) by(1) ,we get

(5r + 100)/(3r + 100) = 11520/9792

( 5r+100)/(3r+100) = 180/153

765r - 540r = 18000 - 15300

225r =2700 => r = 12%

option (c) is correct

Answer 2

The rate of interest is (c) 12%.

Given:

On simple interest, a certain sum becomes 97,920 in 3 years and in 5 years it becomes 1,15,200.

To find:

The rate of interest.

Solution:

To answer this question, we will follow the following steps:

As we know that if P is the principal, R is the rate of interest and 't' is the period then simple interest for 't' years is given by:

$= \frac{p \times r \times t}{100}$

Now,

As given, we have,

On a simple interest,

In 3 years, a certain sum becomes = 97,920

In 5 years, a certain sum becomes = 1,15,200

So,

In 2 years, simple interest is

$= 115200 - 97920$

$= 17280$

(as a principal is the same for both all years)

Now,

The simple interest for 1 year

$= \frac{17280}{2}$

$= 8640$

So,

Simple interest for 3 years

$= 8640 \times 3 = 25920$

Principal amount is

$= 97920 - 25920$

$= 72000$

Now,

Using the formula, we have

P = 72,000

Simple interest for one year = 8640

t = 1 year

$\frac{72000 \times r \times 1}{100} = 8640$

$r = \frac{864}{72}$

$= 12\%$

Hence, the rate of interest is (c) 12%.

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