If you want to measure out exactly one pint of water, and you have only a three pint jug and a five pint jug. How would you do it?
Fill the three pint jug with water and pour it into the five pint jug. Then fill the three pint jug with water once again, and pour it into the five pint jug until it is completely full. The water remaining in the three pint jug is one pint.