Solution #83: Water and Milk

They are both equally contaminated. The water contains exactly as much milk as the milk contains water. The most elegant proof for this celebrated little puzzle is as follows: It does not matter how many transfers are made between the glasses or whether the contents are stirred. Provided that the volumes in the two glasses are equal, then any water in the water glass must be in the milk, there is nowhere else it can be. The milk that it has replaced must be in the water glass. The water glass therefore contains as much milk as the milk contains water.
Source: Sloane, Paul
Categories: Clever, Fractions, Favorite
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