Some of the 50% solution of acid was removed and this was replaced with an equal amount of 20% solution of acid. As a result, a 35% solution of acid was obtained. What fraction of the original solution was replaced?
Choices:
A) 1 / 3	B) 1 / 2	C) 2 / 3	D) 3 / 5	E) 4 / 7

Rationale: let x be the fraction of the original solution that was replaced . 0.5 * ( 1 - x ) + 0.2 ( x ) = 0.35 0.3 x = 0.15 x = 1 / 2 the answer is b .
Answer: B