The simple interest on a sum of money is 1/9 th of the principal and the number of year is equal to the rate percent per annum. The rate of interest per annum is:

 a) 2 %
 b) 7 %
 c) 9%
 d) 10/3 %

Ans: d. Solution Let Principal = x SI = x/9 R = T; R =10/3