Seen on Reddit a few days ago.
An infinite number of mathematicians walk into a bar.
The first one says "I'll have a beer."
The second one says "I'll have half a beer."
The third one says "I'll have one quarter of a beer."
The fourth one says "I'll have one eighth of a beer."
The bartender says "You're all a bunch of idiots!", and he pours two beers.