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Math grouping help

  1. Sep 20, 2008 #1
    1. The problem statement, all variables and given/known data

    Divide 20 students in 4 groups of 5 each. Find the number of ways of doing this?
    Also find how can these gropus be sent to 4 different schools?

    3. The attempt at a solution

    I get both the answers as:

    But my book gives two different answers for the above 2 different question. Help Please!
  2. jcsd
  3. Sep 20, 2008 #2


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    Re: Grouping

    The first answer looks correct: you first pick 5 out of 20 for the first group, then 5 out of the remaining 15 for the second group, etc.

    For the second question, I think you should forget about the students. You have 4 groups, and 4 schools to send them to. In abstract terms: you have 4 balls and 4 slots, how many possible ways are there to put each ball into one slot?
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