Find the principal which yields a simple interest of Rs. 20 and compound interest of Rs. 22 in two years, at the same percent rate per annum?
Select:
A) s . 520	B) s . 480	C) s . 420	D) s . 100	E) s . 200

Rationale: explanation : si in 2 years = rs . 20 , si in 1 year = rs . 10 ci in 2 years = rs . 22 % rate per annum = [ ( ci – si ) / ( si in 1 year ) ] * 100 = [ ( 22 – 20 ) / 20 ] * 100 = 10 % p . a . let the principal be rs . x time = t = 2 years % rate = 10 % p . a . si = ( prt / 100 ) 20 = ( x * 10 * 2 ) / 100 x = rs . 100 answer : d
Answer: D