Question

A sum of money doubles itself in 6 years.Find the rate of simple interest per annum?

Answer 1

Let the sum of money that's principal be x.
Time = 6years
Amount after 6 years becomes double = 2x
Therefor, Simple Interest = Amount - Principal = 2x-x = x
Rate per annum = SI×100/ P×T = x×100/x×6 = 100/6 = 50/3 = 16.66 % approx

Hope that helps

Answer 2

Given :

A sum of money doubles itself in 6 years.

To Find :

The rate of simple interest per annum

Solution :

Let the principle amount be 'x'

So, the amount after 6 years will be 2x

We know, Simple Interest (SI) = Amount (A) - Principle (P)

  Simple Interest (SI) = 2x - x = x

Now,

The formula for simple interest is $\frac{P*R*T}{100}$

where,  P = Principle

            R = Rate

            T = Time

Simple Interest (SI) = $\frac{P*R*T}{100}$

⇒                         x   = $\frac{x * R * 6}{100}$     (∵ SI = x)

⇒                        R   = $\frac{100}{6}$

∴                         R   = 16.67%

∴ The rate of simple interest per annum is 16.67%