if 70% of (x-y) = 30% of (x+y) then what percent of x is y? Choose the most appropriate option: A) 2.5 % B) 40 % C) 5 % D) 15 % E) 25 %

Rationale: "70 % of ( x - y ) = 30 % of ( x + y ) ( 70 / 100 ) ( x - y ) = ( 30 / 100 ) ( x + y ) 7 ( x - y ) = 3 ( x + y ) 4 x = 10 y x = 5 / 2 y therefore required percentage = ( ( y / x ) x 100 ) % = ( ( y / ( 5 / 2 ) y ) x 100 ) = 40 % answer is b ."
Answer: B