In a mixture of 40 liters, the ratio of milk and water is 4 : 1. How much water be added to the mixture…

In $40\text{ litres}$ with Milk : Water $= 4 : 1$, initial Milk $= \frac{4}{5}\times 40 = 32\text{ L}$ and Water $= \frac{1}{5}\times 40 = 8\text{ L}$. Let $x\text{ litres}$ of water be added so the ratio becomes $2 : 3$: $\frac{32}{8 + x} = \frac{2}{3} \implies 16 + 2x = 96 \implies 2x = 80 \implies x = \mathbf{40\text{ litres}}$.