SOLUTION: In a party 15 people shake their hands with each other. How many times did the hand-shake take place?

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Question 776329: In a party 15 people shake their hands with each other. How many times did the hand-shake take place?

Answer by solver91311(24713) About Me  (Show Source):
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Pick one person as the "start". That person can shake hands with 14 different people. Pick the next person. That person can also shake hands with 14 different people, but you have already counted one of those 14 in the 14 that you counted for the "start" person, so only count 13 for person number 2. Then 12 for person number 3...and so on down to the second to the last person who can do 1 unique pairing. So, in sum, add the numbers from 1 to 14. 1 plus 14 is 15. 15 times 14 is 210. 210 divided by 2 is 105. So 105 different handshakes.

John

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