A sum of money amounts to 5 times of itself in 20 years, when invested at a certain rate of simple interest per annum. What is the rate of simple interest per annum that is on offer?

20%

A sum of money amounts to 5 times of itself in 20 years.

Let initial sum = P

Amount after 20 years = 5P

Simple interest = 5P - P = 4P

Simple Interest = \(\frac{Principal ×Rate × Time }{100}\)

4P = \(\frac{P × Rate × 20 }{100}\)

Rate = 20%