Prove that any group of six people contains either 3 mutual friends or 3 mutual strangers.
(For the purpose of this problem any pair of people must be either friends or strangers.)
(In reply to
I don't think it's a question from an IQ test since the answer is a little more involved than what you posted.
If your reasoning were true, it whould work as well for a group of, say, five people, but as TomM has shown, that group can easily have neither 3 mutual friends nor 3 mutual strangers.
As I recall I have gotten this problem from some list online, and I think it came from rec.puzzle before that.
Posted by levik
on 2002-07-02 02:11:03