Two ladies each want to buy two quarts of milk.
One lady has a 5-quart pail and the other lady has a 4-quart pail.
Farmer John, the milkman, has two ten-gallon cans full of milk.
How did he measure out exactly 2 quarts of milk for each lady using only
the 2 pails and the 2 full cans and without spilling any milk?