The milk and water in a mixture are in the ratio 7 : 5. When 15 litres of water are added to it. The ratio of milk and water in the new mixture becomes 7 : 8. The total quantity of water in the new mixture is -

Answer: Option B

According to the question,
$$\text{Milk}:\text{Water}$$
$$\begin{array}{c}7:5\text{hfill}\\ 7:8\text{hfill}\end{array})3\text{unit}$$
∴ Remember water is added and not milk, so make milk equal but here milk is already equal
$$\begin{array}{rl}& \text{3 units = 15 litres}\\ & \text{1 unit = 5 litres}\\ & \text{8 units = 40 litres}\end{array}$$
Total quantity of water in the new mixture = 40 litres