A moderator takes a set of 8 stamps, 4 red and 4 green, known to three logicians, and affixes two to the forehead of each logician so that each logician can see all the other stamps except those two in the moderator's pocket and the two on his or her own head. He asks them in turn if they know the colors of their own stamps:
1. A: "No"
2. B: "No"
3. C: "No"
4. A: "No"
5. B: "Yes"

What are the colors of B's stamps?

red and green

if A and C both have 2 reds each, B would have 2 of the greens. Because he answers NO this cannot be the case. If A has 2 reds and C has 2 greens then; if B has 2 reds C would know he has 2 greens and  If B had 2 greens A would know they had 2 reds. Therefore B must have one of each colour. amy x

Posted by amy on 2004-08-15 16:08:54