How to Get 4 Gallons of Water Using a 3 Gallon & 5 Gallon Jug

By Matthew Burley ; Updated April 12, 2017

Brain teasers are exercises for the brain that are intended to make us think in a different manner than we are accustomed to. Whatever the nature of a brain teaser, it is typically not as simple as it appears to be. Such is the case with the puzzle of how to generate an amount of water that is exactly equal to 4 gallons, when the only tools at our disposal are a 3 gallon jug and a 5 gallon jug.

Solve the Puzzle by Only Filling the 3 Gallon Jug from the Tap

Turn on the water tap, then proceed to completely fill the 3 gallon jug.

Pour the contents of the 3 gallon jug into the 5 gallon jug, then fill the 3 gallon jug again.

Pour the contents of the 3 gallon jug into the 5 gallon jug until it is full, leaving 1 gallon of water in the 3 gallon jug.

Empty the contents of the 5 gallon jug, then pour the 1 gallon of water from the 3 gallon jug into the 5 gallon jug.

Fill the 3 gallon jug, then add those 3 gallons to the 1 gallon already in the 5 gallon jug for a total of 4 gallons.

Solve the Puzzle by Only Filling the 5 Gallon Jug from the Tap

Turn on the water tap, then fill the 5 gallon jug.

Fill the 3 gallon jug with the water from the 5 gallon jug, leaving 2 gallons in the 5 gallon jug.

Empty the contents of the 3 gallon jug, then pour the remaining 2 gallons from the 5 gallon jug into the 3 gallon jug.

Fill the 5 gallon jug completely.

Pour 1 gallon from the 5 gallon jug into the remaining space in the 3 gallon jug, leaving 4 gallons in the 5 gallon jug.

Warning

If you are performing this puzzle in real life, be careful when lifting a full, 5 gallon jug of water. Since a pint of water weighs 1 pound and there are 8 pints in a gallon, that 5 gallon jug weighs 40 pounds, plus the weight of the jug.

About the Author

Matthew Burley has been a writer of online content since 2005. You can view many of his articles on associatedcontent.com. Burley holds a Bachelor of Science in political science from Arizona State and a Master of Science in computer information systems from the University of Phoenix.