Here's one: You have two containers of the same size - one is filled with milk and the other is filled with the exact same amount of water. Let's say Container A has milk and Container B has water. You take one cup of milk from Container A and mix it in Container B. Then you take one cup of the milk/water mixture in Container B and mix it in Container A. Considering that milk and water is evenly distributed when mixed, does Container A have more water or does Container B have more milk?