Warden Smith has been transferred to yet another prison, and pity his new set of prisoners!
This time he announces that: tomorrow ...
they will be taken to the courtyard and arranged in a circle. each prisoner will be given a white or black hat as determined by a fair-coin toss. each prisoner will be able to see the hats on all the other prisoners. no prisoner will be able to see his own hat. no communication will be permitted.
Then,
unless at least one prisoner guesses, and every prisoner who does guess guesses correctly, all the prisoners will be executed.
That is, if they all pass, or if anyone guesses incorrectly, they're all dead.
That makes the prisoners desperate enough to call you in as a consultant.
You meet with them the night before the event, to advise them what to do.
One prisoner suggests that they will have an even chance of survival if one person guesses, and all the others pass.
What do you advise?
Edit - added 4:50 pm EDT 30 May 2008
Starter suggestion - suppose there are only 3 prisoners.
Work out strategies that might improve on the 50% that seems intuitive.
Then try out your strategy for 16 15 prisoners, where survival could be quite likely.