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Logic and Stamps (Posted on 2004-07-31) Difficulty: 4 of 5
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?

See The Solution Submitted by Brian Smith    
Rating: 2.5000 (8 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution No thinking needed | Comment 4 of 17 |
Given that the problem is symmetric (there are as many red stamps as green ones), if the solution was Red-Red, then it could also be Green-Green, so if someone could reason his colors and reach an unique solution, it must have been RED-GREEN.
  Posted by Federico Kereki on 2004-08-02 07:37:12
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