Technology

Can You Solve the Water Puzzle?

January 26, 2016 | Elizabeth Knowles

if you have a 9-cup glass and a 4-cup glass and an endless supply of water, how can you measure out 6 cups of water into the bigger one without approximating?

Give it a try!

Puzzles like this one have been especially popular since the famous one in the movie Die Hard with a Vengeance. In that case, the puzzle challenged viewers to measure out 4 gallons using a 3-gallon and a 5-gallon jug.

Here, you are using a 4-cup (blue) glass and a 9-cup (red) glass to measure out 6 cups of water.

Here’s one way to do it:

Fill the red glass with 9 cups of water. Empty it into the blue glass twice so that you are left with 1 cup of water. Dump that into the blue glass. Fill up the red one again. Empty as much as you can (3 cups) into the blue glass and you will be left with 6 cups.

Red Glass (9 cups)	Blue Glass (4 cups)	Action
0	0	Fill the red glass
9	0	Transfer 4 cups to the blue glass
5	4	Empty the blue glass
5	0	Transfer 4 cups to the blue glass
1	4	Empty the blue glass
1	0	Transfer the remaining water from the red glass to the blue one
0	1	Fill the red glass
9	1	Empty what you can into the blue glass
6	4	You have 6 cups in the red glass!