Some part of the 50% solution of acid was replaced with the equal amount of 30% solution of acid. As a result, 40% solution of acid was obtained. What part of the original solution was replaced?
Answer is C. It's relatively easy to understand why 1/2 is correct but I can't logically put an equation together to solve the question.
x is part of solution replaced
0.5 (1-x) +0.3*x = 0.4*1
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