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    • Thread Starter
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    Hi, the following question has got me.
    7 people are to be seated in a row. Calculate the number of ways in which this can be done so that 2 particular people A and B always have exactly one of the others between them (note the answer from the book is 1200)
    I just dont know how to get this.
    any help greatly appreatiated
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    Consider A - B - - - -,. How many ways can this be done?
    Then - A -B - - - etc.
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    and don't forget B _ A _ _ _ _, _ B _ A _ _ _, etc.
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    Think of A?B as one unit, then you 5 things to arrange ... do you know how many ways there are for this

    Then double because of B?A

    Then x5 because ? could be 5 different people
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    (Original post by TenOfThem)
    Think of A?B as one unit, then you 5 things to arrange ... do you know how many ways there are for this

    Then double because of B?A

    Then x5 because ? could be 5 different people
    Thanks 10 of them , yours was the best one .
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    (Original post by BabyMaths)
    and don't forget B _ A _ _ _ _, _ B _ A _ _ _, etc.
    Thanks baby maths - great help
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    (Original post by Matureb)
    Consider A - B - - - -,. How many ways can this be done?
    Then - A -B - - - etc.
    Thanks for the help matureb
 
 
 
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