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 choice from the following answers.
A) 1/5  B) 1/4  C) 1/2  D) 3/4  E) 4/5
Original Acid : Total ratio = 50:100 . let us say you replaced x part of this. So you are left with (1-x) of the original. So volume of acid left is (1-x)50.   in the new solution.. you added x of 30% solution. i.e 30x acid   (1-x)50 + 30x is the volume of acid. The total volume is still 100. And this concentration is 40%   [(1-x)50 + 30x] / 100 = 40/100   solve to get 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?