SOLUTION: i have invited nine people to a party. They all shake hands with me, and each pair shake hands. how many hand shakes are there? 9+8+7+6+5+4+3+2+1=45 how many hand shakes would th

Question 999315: i have invited nine people to a party. They all shake hands with me, and each pair shake hands. how many hand shakes are there?
9+8+7+6+5+4+3+2+1=45
how many hand shakes would there be if i invited n-1 people?
I organise another party with 9 guests and myself. some pairs shook hands, but some did not. no pair shook hands more than once. Must there be two people who shook hands with the same number of people? what if i had invited n-1 people?
Thank you
Answer by ikleyn(52784) (Show Source): You can put this solution on YOUR website!
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i have invited nine people to a party. They all shake hands with me, and each pair shake hands. how many hand shakes are there?
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The answer is . (, if you know what does it mean).

If n = 9+1 = 10, then the number of hand shakes is = 45.

This is very standard problem on combinations.

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