A 60-litre mixture contains milk and water in the ratio 2:1. How many litres of the mixture should be withdrawn and replaced with water to make the ratio 1:2? MCQ with Answer and Explanation

Milk=40 L, water=20 L. Withdraw x L mixture: milk removed = (2/3)x, water removed = (1/3)x. After replacement, milk = 40 - 2x/3, water = 20 - x/3 + x = 20 + 2x/3. Ratio 1:2 → (40 - 2x/3)/(20 + 2x/3) = 1/2 → 2(40 - 2x/3) = 20 + 2x/3 → 80 - 4x/3 = 20 + 2x/3 → 60 = 2x → x = 30.