glass 1 has 2/3 of a glass milk and 1/3 of a glass water

glass 2 has 1/2 of a glass of milk and 1/2 of a glass water.

So the mixture in glass 3 (assuming it lage enough to contain the contents of both glass 1 and glass 2 and that glasses 1 and 2 are of equal volumes) has (2/3)+(1/2) of a glass of milk and (1/3)+(1/2) of a glass of water.

So the ratio of milk to water in the mixture is ((2/3)+(1/2)) : ((1/3)+(1/2))

CB