duuuma wrote:

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?

A. \(\frac{1}{5}\)

B. \(\frac{1}{4}\)

C. \(\frac{1}{2}\)

D. \(\frac{3}{4}\)

E. \(\frac{4}{5}\)

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

x=1/2

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