An infinite number of mathematicians walk into a bar. The first one orders a beer. The second one orders half a beer. The third one orders a fourth of a beer. The bartender stops them, pours two beers, and says, "You guys should know your limits."
Mathematicians and Their Limits
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Explanation
Experiment
The joke plays on the mathematical concept of a converging series. The mathematicians are ordering fractions of beer that get smaller and smaller, and if you added them all up, it would approach a finite limit of two beers. The bartender is making a pun by telling the mathematicians they should "know their limits" – a math term, as well as a saying about knowing when to stop.