Question 782205
In the movie, Die Hard with a Vengeance, the hero was told that in order to stop an explosion from taking place he would have to place a plastic jug with exactly four gallons of water in it on a scale.  The wrong weight would set off the big bang.  Unfortunately, the villain had left the hero only two jugs, one that would hold exactly 3 gallons and one that would hold exactly 5 gallons.  There was a fountain nearby with lots of water in it.  Explain how to get exactly four gallons into the five gallon container.
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Fill the 5 gal jug
Pour 3 gal into the 3 gal jug, leaves 2 gals
Dump the 3 gal jug, pour the 2 for the 5 gal jug into it.
Fill the 5 gal jug.
Fill the 3 gal jug from the 5 gallon jug.
4 gallons remain in the 5 gallon jug.