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Smart prisoners always get a break (Posted on 2002-08-27) Difficulty: 4 of 5
100 prisoners are put into solitary cells. There's a central living room with one light bulb; the bulb is initially off. No prisoner can see the light bulb from his or her own cell. Every day, the warden picks a prisoner at random, and that prisoner goes to the central living room. While there, the prisoner can toggle the bulb if he or she wishes. Also, the prisoner has the option of asserting the claim that all 100 prisoners have been to the living room. If this assertion is false (that is, some prisoners still haven't been to the living room), all 100 prisoners will be shot for their stupidity. However, if it is indeed true, all prisoners are set free and inducted into MENSA, since the world can always use more smart people. Thus, the assertion should only be made if the prisoner is 100% certain of its validity.

The prisoners are allowed to get together one night, to discuss a plan. What plan should they agree on, so that eventually, someone will make a correct assertion?

(From http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml)

See The Solution Submitted by levik    
Rating: 4.3636 (11 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
This seems stupidly easy... | Comment 18 of 23 |
Every night at the meeting, ask anyone who's been in the living room to raise their hand. If you count 100, tell everyone that whoever goes the next day should say everybody went.
  Posted by thegnome54 on 2006-02-09 16:00:40
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