I saw this yesterday. I'm not that much into puzzles, but this is amazing:
The names of 100 prisoners are placed in 100 wooden boxes, one name to a box, and the boxes are lined up on a table in a room. One by one, the prisoners are led into the room. They may look into up to 50 of the boxes to try to find their own name, but must leave the room exactly as it was.The prisoners are permitted no further communication after leaving the room. They do have a chance to plot a strategy in advance. Good thing. Unless they all find their own names, they will all be executed.
If each prisoner examines 50 boxes at random, the probability of the group's survival is a miniscule (1/2)^100, or about 0.00000000000000000000000000000008. Even worse, if they all happen to look into the same 50 boxes, their chances drop to zero.
The 'winning strategy' improves the odds to almost 1/3, which is about 30 orders of magnitude better. And its stunningly obvious ... in retrospect. [Actually, I had to mull over the answer for quite a while to figure out why it worked, so I guess that's not true.] More puzzles (and solutions) here.
Hat Tip to Geekpress.