Question

A sum of Rs. 1200 at simple interest doubles itself in 8 years. The rate of interest is _ percentage per year.

Answer 1

Let the Principal be Rs.100

Required Amount-Rs.200

Required SI= Rs.100

SI=P×R×T/100
100=100×R×8/100
100/8=R
12.5=R

The Rate Of Interest is 12.5%

Answer 2

Answer:

The rate of interest is 12.5% per year.

Step-by-step explanation:

Formula

$Simple\ interest = \frac{Principle\times Rate\times Time}{100}$

Amount = Simple interest + Principle

As given

A sum of Rs. 1200 at simple interest doubles itself in 8 years.

Thus

Amount = 2 × Principle

             = 2 × 1200

Amount = Rs 2400

Thus

2400 = 1200 + Simple interest

Simple interest = 2400 - 1200

Simple interest = Rs 1200

Put all the values in the formula

$1200 = \frac{1200\times Rate\times 8}{100}$

$1200 = \frac{9600\times Rate}{100}$

$Rate = \frac{1200\times 100}{9600}$

$Rate = \frac{120000}{9600}$

Rate = 12.5%

Therefore the rate of interest is 12.5% per year.