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Old 01-14-2018, 10:23 PM
Shinigami99 Shinigami99 is offline
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Join Date: Feb 2013
Posts: 10
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Given:
1. There are 3 people.
2. They would have a green/red cross on their forehead.
3. They can only see the other peoples' foreheads.

Based on the given, the only possible scenarios where all three people would raise their hands are when 2 or 3 people have green crosses on their forehead.

Now, if it was 2 people who had green crosses on their forehead, the two people who had green crosses would immediately know what color the cross on their own forehead is, based on the fact that all three people raised their hands.

Chuckles, upon seeing that the other 2 didn't immediately answer, was therefore confident that the cross on his own forehead must also be green.
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