Kajal invested Rs. (y+2000) on compound interest at the rate of 18% per annum compounded annually in scheme P. She invested Rs. ‘y’ on 20% per annum on simple interest in scheme Q. After two years, if the interest obtained from scheme P is Rs. 739.2 more than the interest obtained from scheme Q, then find out the value of ‘y’.

Solution

Kajal invested Rs. (y+2000) on compound interest at the rate of 18% per annum compounded annually in scheme P. Interest after 2 years from scheme P = (y+2000) of (100+18)% of (100+18)% - (y+2000) = (y+2000) of 118% of 118% - (y+2000) = (y+2000) x 1.18 x 1.18 - (y+2000) = 1.3924(y+2000) - (y+2000) = (y+2000)x[1.3924 - 1] = 0.3924(y+2000) She invested Rs. ‘y’ on 20% per annum on simple interest in scheme Q. Interest after 2 years from scheme Q = y x 20% x 2 =  0.4y After two years, if the interest obtained from scheme P is Rs. 739.2 more than the interest obtained from scheme Q. 0.3924(y+2000) = 0.4y+739.2 0.3924y+784.8 = 0.4y+739.2 784.8-739.2 = 0.4y-0.3924y 0.0076y = 45.6 Value of ‘y’ = 6000