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Math Help - combinatorics

  1. #1
    Junior Member
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    combinatorics

    i am confused about this one
    At a family runion everyone shakes everone elses hand once, if a total of 190 handshakes take place,how many people were at the reunion?

    and one more what is a constant ter in the expansion of (x+2)^9
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  2. #2
    Junior Member
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    IF everybody shook hands atleast once then there were nC2 handshakes since it takes 2 people to shake hands

    => [n(n-1)]/2=190
    n(n-1)=380

    or n=20

    SO 20 people were present
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