Answers

2014-03-31T09:33:28+05:30
Principle : Pigeon Hole principle


Explanation :
A person can shake hands with between 0 and N-1 people since you cannot shake hands with your self. That is N possibilities. If one person has shaken hands with everyone else, then there is no one who hasn’t shook hands with no one ( means all have shook hands with at least 1 ) . And the other way around. So 0 and N-1 possibilities are mutual exclusive. So we are down to N-1 possibilities of people each person can shake hands with.

So if there are N people and N-1 possibilities to the number of people each person can shake hands with then  by Pigeon Hole principle at least 2 people have shook hands with an equal amount of people
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