A sum of money amounts to Rs. 8940 after 7 years and Rs.11040 after 12 years at the same rate of simple interest. The rate of interest per annum is:

 a) 7 %
 b) 8 %
 c) 9 %
 d) 11 %

7 %. Solution Simple Interest for 5 years = (11040 - 8940) = Rs. 2100 Simple Interest for 7 years = (2100 x 7)/5 = Rs. 2940 Principal amount = 8940 - 2940 = Rs. 6000 R = (SI x 100)/PR = (100 x 2940)/(6000 x 7) = 70%