Sharing water

Puzzle

After wandering around lost in the desert two travelers come across a magic refrigerator. Inside, they find a jug full to the rim of eight cups of ice cold water. Additionally, there are two empty jugs, one which can hold exactly three cups, and one which can hold exactly five cups.

The travelers, although very thirsty, realize that it is important to divide the water up fairly. How can they do so using only the three jugs?

Help

Hint

Just try it. Really.

Answer

Fill up the 3 cup jug, and then transfer the contents to the 5 cup jug.

Then fill up the 3 cup jug again, and transfer 2 of these cups to the 5 cup jug. Empty the 5 cup jug back into the eight cup jug, and pour the 1 cup still in the 3 cup jug into the 5 cup jug.

Fill up the 3 cup jug and pour it into the 5 cup jug, leaving 4 cups in the 5 cup jug and 4 in the original 8 cup jug.

See also

Die Hard III

References

Although this puzzle is quite old, I first came across it on Cut the Knot.