Some part of the 50% solution of acid was replaced with the equal amount of 30% solution of acid. As a result, 40% solution f acid was obtained. what part of the original solution was replaced? Choose the correct choice
A) 1/5
B) 1/4
C) 1/2
D) 3/4
E) 4/5
Let X = Part of acid solution replaced, then 1-X will be the parts not replaced.   (1-X)*0.5 + 0.3*x = 0.4   0.5 - 0.5X +0.3X = 0.4   -0.2X = -0.1   X=1/2   So the answer is 1/2
<result>C</result>
Some part of the 50% solution of acid was replaced with the equal amount of 30% solution of acid. As a result, 40% solution f acid was obtained. what part of the original solution was replaced?