The difference between the compound interest and simple interest on a certain sum at 10% per annum for 2 years is Rs. 631. Find the sum.

Let the sum be Rs. x. Then,

            C.I. = x ( 1 + ( 10 /100 ))² - x = 21x / 100 ,

            S.I. = (( x * 10 * 2) / 100) = x / 5

            (C.I) - (S.I) = ((21x / 100 ) - (x / 5 )) = x / 100

             ( x / 100 ) = 632 , x = 63100.

             Hence, the sum is Rs.63,100.