← Paradoxes & riddles
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Ants on a Ruler
a puzzle with a clever shortcut
Ants on a one-meter ruler walk at one centimeter per second, turning around whenever two collide. How long until every ant has fallen off? The chaos hides a shortcut: a collision looks exactly like two ants walking straight through each other.
Source: The classic ants-on-a-stick puzzle, dramatized
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