A sum of money becomes 6 times in 25 years at simple interest. Find the rate of interest per annum.

20% 15% 16% 25%

20%

ATQ, Principal : Amount       1      :      6              =  5 (S.I.) Total Rate of interest in 25 years = \(\frac{5}{1}\) × 100 = 500% Rate of interest per annum =  \(\frac{500}{25}\)  =  20%