If the simple interest on a sum of money for 2 years at 5% per annum is Rs. 40, what is the compound interest on the same sum at the rate and for the same time?  Choose one.
A) s . 41.00
B) s . 51.22
C) s . 51.219
D) s . 41.18
E) s . 51.11

Rationale: "explanation : sum = ( 40 * 100 ) / ( 2 * 5 ) = rs . 400 amount = [ 400 * ( 1 + 5 / 100 ) 2 ] = rs . 441 c . i . = ( 441 - 400 ) = rs . 41 answer : a"
Answer: A