Insight · ★★☆☆☆ · ~5 min
The Water Pouring Puzzle
A 5-liter jug, a 3-liter jug. Can you measure exactly 4? (Die Hard says yes.)
by MindYourPuzzle
A puzzle made famous by a Hollywood scene (Die Hard 3) — but the real magic is the number theory underneath.
You have two unmarked jugs: one holds exactly 5 liters, the other exactly 3 liters, and an unlimited water supply. You can fill a jug to the top, empty it completely, or pour from one into the other until either the source is empty or the destination is full.
Can you measure out exactly 4 liters — yes or no?
(Answer "yes" or "no".)
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