The simple interest on a sum of money is \(\frac{8}{25}\) of the sum. If the number of years is numerically half the rate percent per annum, then the rate percentt per annum is:

8%

Say, Sum = 25

S.I. =  8

here, Time = \(\frac{1}{2}\) x rate 

⇒ 8 = \(\frac{25 × R × R}{100 × 2}\)

⇒ 8 = \(\frac{R^2}{8}\)

⇒ Rate of interest = \(\sqrt {64}\) = 8%