What is the approximate rate of simple interest per annum, if a sum of money becomes 6 times of itself in 15 years?

33.33%

Given :-

Sum becomes 6 times of itself in 15 years .

Let sum = P , then  Amount = 6P 

Simple interest of 15 years= 6P - P = 5P

Simple interest of 1 year = \(\frac{5P }{15}\)  = \(\frac{P }{3}\)

We know ,

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

\(\frac{P }{3}\)  = \(\frac{P × Rate × 1 }{100}\) 

Rate = 33.33%