The difference between the compound interest and simple interest on a certain sum at 10% per annum for 2years is $631. Find the sum?	Answers.
A) $ 52000
B) $ 61000
C) $ 71540
D) $ 63100
E) $ 56210

Rationale: let the sum be $ x c . i . = x ( 1 + 10 / 100 ) ^ 2 - x = 21 x / 100 s . i . = ( x * 10 * 2 ) / 100 = x / 5 c . i . - s . i . = ( 21 x / 100 ) - ( x / 5 ) = x / 100 x / 100 = 631 x = 63100 answer is d
Answer: D