If the total simple interest received on a sum for 25 years is $\frac{5}{8}$ of the principal, what is the rate of simple interest paid per annum?

2.5%

Simple Interest is \(\frac{5}{8}\) of principal.

Let Principal = 8 & Simple interest = 5

We know ,

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

5 = \(\frac{8×Rate × 25 }{100}\)

Rate = \(\frac{5 }{2}\)%

= 2.5%