Some of the 50% solution of acid was removed and this was replaced with an equal amount of 30% solution of acid. As a result, a 40% solution of acid was obtained. What fraction of the original solution was replaced?
Pick one:
A) 1 / 2	B) 1 / 3	C) 2 / 3	D) 1 / 4	E) 2 / 5

Rationale: "let x be the fraction of the original solution that was replaced . 0.5 * ( 1 - x ) + 0.3 ( x ) = 0.4 0.2 x = 0.1 x = 1 / 2 the answer is a ."
Answer: A