Originally Posted by JARblue

Fill the 5 gallon jug. Fill 3 gallon jug from the 5 gallon jug leaving you two gallons in the 5 gallon jug. Empty the 3 gallon jug and pour the two gallons into it from the 5 gallon jug. Fill up the 5 gallon jug again and then pour enough to fill the 3 gallon jug. Since you already have two gallons in the 3 gallon jug, you have just poured one gallon into the 3 gallon jug leaving four gallons left in the 5 gallon jug.


TL;DR??

Math.