3 white guys
Three white men were taken captive by a hostile Indian tribe. The chieftain was willing to let them go so he took them to a tepee, where there was no light. He put one head band on each of their heads (he had 3 white and 2 red - so 2 head bands were not used - captives were informed about these numbers). Then they went out in a queue so that each man saw the head-band of those standing in front of himself (the first one did not see any head band, the second one saw the first one'* head band, and the third one saw the head bands of the two others). If somebody said the colour of his head-band, they all would be free. After a quiet while one of them (the one in front who could not see any of the others) said: "My head-band is ...".
What colour was his head band? And how would you reason it?
You have to assume that all the prisoners are fairly intelligent and have confidence in the intelligence of their fellow prisoners.
An incorrect guess deems them to imprisonment.
Only one guess can be made by the group.