Question

Find the rate of interest per annum if the sum of money becomes five times the principal in 10 years.​

Answer 1

Answer :-

Given :-

• Amount = 5 × sum
• Time = 10 years

To Find :-

• Rate of interest

Solution :-

Let the sum be x

Amount = 5x

→ Simple interest = Amount - sum

→ SI = 5x - x

→ SI = 4x

Now, we have -

• Sum = Rs. x
• SI = Rs. 4x
• T = 10 years

Substituting the value in formula :-

→ $\sf SI = \dfrac{PRT}{100}$

→ $\sf 4x = \dfrac{x \times 1\cancel0 \times R}{10\cancel0}$

→ $\sf 4\cancel x = \dfrac{\cancel x \times R}{10}$

→ $\sf 4 = \dfrac{R}{10}$

→ $\sf R = 4 \times 10$

→ $\sf R = 40$

Rate of interest = 40% p.a.