The difference between the compound interest and simple interest on a certain sum at 10% per annum for 2years is $631. Find the sum?  Choose the correct option
A) $52000  B) $61000  C) $71540  D) $63100  E) $56210
Let the sum be $x   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 = 631   x = 63100   Answer is $63100
<result>D</result>
The difference between the compound interest and simple interest on a certain sum at 10% per annum for 2years is $631. Find the sum?