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?
1/5
1/4
1/2
3/4
4/5
Question is from GMAT club but it is from their MGMAT challenge set.
(C) 2008 GMAT Club