A vessel contained a solution of acid and water, in which water was 64%. Four litres of the solution was taken out of the vessel and the same quantity of water was added. If the resulting solution contains 30% acid, the quantity (in litres) of the water in the solution, at the beginning in the vessel, was:

Answer: Option B

Solution

Answer: Option B

Solution:

\begin{array}{*{20}{c}} {}&{{\text{Acid}}}&{{\text{Water}}} \\ {{\text{Old}} \to }&{36\% }&{64\% } \\ {{\text{New}} \to }&{30\% }&{70\% } \end{array}

$$\begin{array}{rl}& \text{Old mixture}=\text{Remaining}+\text{Taken out}\\ & =20\text{L}+4\text{L}\\ & =24\text{L}\\ & \text{Water}=24\times \frac{64}{100}\Rightarrow 15.36\text{L}\end{array}$$