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

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