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?
a 1/5
b 1/4
c 1/2
d 3/4
e 4/5
a 1/5
b 1/4
c 1/2
d 3/4
e 4/5
