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Thread: probability again (how many groups of at least 2 people...)

  1. #1
    Junior Member
    Join Date
    Jan 2006
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    58

    probability again (how many groups of at least 2 people...)

    Hi, the question asks.

    How many groups consisting of at least 2 people can be chosen from a group of 10 people?

    I tried...

    10!/2!2!2!2!2! Thinking that 5 groups can be formed but got the wrong answer.

  2. #2
    Elite Member
    Join Date
    Jan 2005
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    7,570

    Re: probability again

    Quote Originally Posted by thelazyman
    How many groups consisting of at least 2 people can be chosen from a group of 10 people?
    I am not doing this completely. Here are hints.
    ‘Groups’ in this context are subsets!
    If there are N elements in a set, then there are 2<SUP>N</SUP> subsets of that set.
    Now one of those sets is the empty set - the null-group no members.
    There are N singletons set, subsets with only one element.
    Now you combine those along with what you learned from the dice problem and finish it this off. Post your answer and we will check it.
    “A professor is someone who talks in someone else’s sleep”
    W.H. Auden

  3. #3
    Guest
    is it 2^10 - 10?

  4. #4
    Elite Member
    Join Date
    Jan 2005
    Posts
    7,570
    Quote Originally Posted by Anonymous
    is it 2^10 - 10?
    Actually it is [tex]\L
    2^{10} - 11[/tex]

    Think about why 11!
    “A professor is someone who talks in someone else’s sleep”
    W.H. Auden

  5. #5
    Guest
    total - 1 - 0
    2^10 -10 -1

    cool, thanks

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