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Probability of girls sit together/ seperated

  1. Jul 6, 2014 #1
    1. The problem statement, all variables and given/known data

    Ten Students sit in a row. Find the probability of 6 boys and 4 girls can be arranged if (i) all girls are side by side?
    (ii) all girls are seperated by boys


    2. Relevant equations



    3. The attempt at a solution

    my working for part i is 4!x7!=120960

    for part ii, why cant i just take 10! -120960=3507840 ? the ans given is 604800
     
  2. jcsd
  3. Jul 6, 2014 #2

    Fredrik

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    Part (i) looks OK to me. (7 possible positions for the first girl, 6! ways to order the boys in the remaining positions). If you take 10! minus the result of part (i), what you find is just the number of ways to not have four girls in a row. This includes e.g. gggbgbbbbb which has three girls next to each other, but the problem is asking for arrangements like gbgbbgbgbb, where no two girls are next to each other.
     
    Last edited: Jul 6, 2014
  4. Jul 7, 2014 #3

    HallsofIvy

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    Your question "Find the probability of 6 boys and 4 girls can be arranged" doesn't really make sense. From what you do, it appears that the question was really "Find the number of different ways 6 boys and 4 girls can be arranged".
     
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