# If 12 people are playing in a tournament and?

If 12 people are playing in a tournament and each person plays every other person, how many games will be played?

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1. Mrs. Sue??

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2. Reiny

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3. The first person plays 11, the second plays 10, the thrid plays 9

number games=11+10+9+...+1
the sum of numbers from n-1 to 1, or
number= N*(n-1)/2=12*11/2= 66

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4. number of subsets of 2 elements from a sample space of 12
= C(12,2) = 66

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posted by Reiny
5. n*(n-1)/2

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posted by aa
6. 66 people. Just do 132 / 2.

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