If the diameter of circle R is 50% of the diameter of circle S, the area of circle R is what percent of the area of circle S?  Answers
A) 35 % B) 25 % C) 20 % D) 15 % E) 10 %

Rationale: "let diameter of circle r , dr = 50 and diameter of circle s , ds = 100 radius of circle r , rr = 25 radius of circle s , rs = 50 area of circle r / area of circle s = ( pi * rr ^ 2 ) / ( pi * rs ^ 2 ) = ( 25 / 50 ) ^ 2 = ( 5 / 10 ) ^ 2 = 25 % answer : b"
Answer: B