SOLUTION: ther were 20 people in the house each shake one another. how many hand shakes took place

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Question 585046: ther were 20 people in the house each shake one another. how many hand shakes took place
Answer by stanbon(75887) About Me  (Show Source):
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ther were 20 people in the house each shake one another. how many hand shakes took place
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Procedure: Try it with small numbers.
2 people: 1
3 people: 2+1 = 3
4 people: 3+2+1 = 6
5 people: 4+3+2+1 = 10
6 people: 15
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20 people: 19+18+...+1
Sum = (n/2)(a+n) = (19/2)(1+19) = 190
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Cheers,
Stan H.