Some part of a 50% solution of acid was replaced with an equal amount of 30% solution of acid. If, as a result, 40% solution of acid was obtained, what part of the original solution was replaced? Choose the correct option.
A) 1/5  B) 1/4  C) 1/2  D) 3/4  E) 2/3
Original Removed Added Result   1/2oncentration 0.50 0.50 0.70 0.60   Amount 1 x x 1   Multiply 0.50 0.50x 0.70x 0.60   0.50 (Original amount) - 0.50x (Removed) + 0.70x (Added) = 0.60 (End Result)   0.20x = 0.10   x = 1/2   ANSWER:1/2
<result>C</result>
Some part of a 50% solution of acid was replaced with an equal amount of 30% solution of acid. If, as a result, 40% solution of acid was obtained, what part of the original solution was replaced?