Step 1: Fill the 5 gallon jug and then pour it into the 3 gallon jug. The 5 gallon jug has
2 gallons left.
Step 2: Now throw the 3 gallon water away. Pour the 2 gallons from the 5 gallon jug to the 3 gallon jug. So now the 3 gallon jug has just 2 gallons of water.
Step 3: Fill the 5 gallon jug again, and pour 1 gallon to the 3 gallon jug. What do u have left in the 5 gallon jug? 4 gallons of water!