MAT Exam 2021 Paper

Concept:Replacement changes the water content by removing some original mixture and adding the new mixture.Explanation:Let the total capacity of the jar be $1$ unit.Let the fraction of milk replaced be $x$.Initial water in the jar $= 40\% = 0.4$ units.Water removed with the replaced part $= 0.4x$.Water added from the second liquid contains $19\%$ water, so added water $= 0.19x$.Final water content is $26\% = 0.26$ units.Thus, $0.4 - 0.4x + 0.19x = 0.26$.Simplify: $0.4 - 0.21x = 0.26$.So, $0.21x = 0.14$.Hence, $x = \frac{0.14}{0.21} = \frac{2}{3}$.Answer:$\frac{2}{3}$, i.e. option A.