One may solve it by alligation as well.

50 30

\ /

40

/ \

10 10

50 - Percent of acid in first solution

30 - Percent of acid in second solution

40 - Percent of acid in mixture of both

LHS 10 -> Percent of acid in mixture of both - Percent of acid in second solution = 40-30 -> Portion of the second in the mixture

RHS 10 -> Percent of acid in first solution - Percent of acid in mixture of both = 50-40 ->Portion of the first in the mixture

\(\frac{Portion \quad of \quad second}{Portion \quad of \quad first}=\frac{10}{10}=\frac{1}{1}\)

\(\frac{Portion \quad of \quad first}{Total \quad mixture}=\frac{1}{1+1}=\frac{1}{2}\)

If the new mixture contains 1/2 of the first solution; then half of the first solution must have been replaced with second solution.

Ans: "C"

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~fluke

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