I got a surprising amount of emails about this post, with requests for more such puzzles, so here you go (answers after the jump).
1. A deaf-mute man walks alone up to a movie theater counter shortly before a matinee which costs 50 cents to enter. Making no particular gesture (and obviously, saying nothing), he hands the clerk a dollar. Rather than giving him 50 cents in change, the clerk hands him two tickets. The man smiles and nods his thanks. How did the clerk know that he wanted two tickets rather than one?
2. Four people are fleeing the zombie apocalypse in the dark of night, and have to get across a narrow bridge in 17 minutes to survive. The bridge is so rickety that no more than two people can stand on it at any one time or it will collapse. It is also full of holes such that it can only be safely crossed while holding a flashlight. The 4 people have only one flashlight between them. A further challenge is that the 4 people are of different ages and levels of health, such that it takes each a different amount of time to cross the bridge. One takes 10 minutes, one needs 5 minutes, one needs 2 minutes, and one needs 1 minute (all invariably, i.e., no amount of help from a faster person can speed a slower person up). How do the 4 people manage to save their lives by crossing their entire party in the 17 minutes available?
3. A man with a heart condition has to take two medications at the same time every 4 hours or he will die. The medication regime is hard to follow: If he takes none or just one of the needed pills at the appointed time, or he takes that more than 1 of either pill within each 4 hour block, he will have a fatal heart attack. To add to the complexity, the pills of each medication are exactly the same in every respect – color, shape, size, texture, weight, labeling. He copes with this challenge by keeping each medication in its own, clearly labelled pill bottle.
While at his hunting lodge in Northern California, something terrible happens. Just before he is about to take his medications, a earth tremor hits and he falls over. The tremor passes quickly, but unfortunately all but 2 pills have fallen out of one bottle and all but 3 have fallen out of the other. Every other pill is scattered on the floor and he can’t tell them apart! It’s a two day trip back to town where he can help from his pharmacist and doctor, and he has no phone, so he has to figure out how to keep himself alive until he can return to town. How does he do it?
4. 4. A man hands a bank teller a check with the symbols “O – O X +” written on the back. The teller says “Oh, I see you are in the navy!”. Why?