The ratio of milk to water in three containers of equal capacity is 3 : 2, 7 : 3 and 11 : 4 respectively. The contents of the three containers are mixed together. What is the ratio of milk to water after mixing ?

$$\eqalign{ & {\text{Milk in the mixture}} \cr & = \left( {\frac{3}{5} + \frac{7}{{10}} + \frac{{11}}{{15}}} \right){\text{units}} \cr & = \frac{{61}}{{30}}{\text{units}}{\text{.}} \cr & {\text{Water in the mixture}} \cr & = \left( {\frac{2}{5} + \frac{3}{{10}} + \frac{4}{{15}}} \right){\text{units}} \cr & = \frac{{29}}{{30}}{\text{units}}{\text{.}} \cr & \therefore {\text{Required ratio}} \cr & = \frac{{61}}{{30}}:\frac{{29}}{{30}} \cr & = 61:29 \cr} $$