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    Permutations and Combinations

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    Ahmed
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    Permutations and Combinations

    Post by Ahmed on Sat Apr 10, 2010 7:26 pm

    I am up to the worst thing in math IMO. So if anyone could help it would be appreciated.
    ======================
    In how many ways can four men and four women be seated in a row of eight seats if:

    (a) The women are to be seated together, and the men are to be seated together?
    (b) They are to be seated alternately by gender.


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    preid1220
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    Re: Permutations and Combinations

    Post by preid1220 on Sun Apr 11, 2010 12:12 pm

    my head hurts.


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    The Banker
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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 2:00 pm

    for (a) is it all the women seated together and all them men seated together?
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 2:08 pm

    I don't get what you are saying Marwa...?


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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 2:11 pm

    like do the women have to sit together in groups of 4 or can we gave 2 groups of 2?
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 2:15 pm

    The women have to sit together.


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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 2:16 pm

    well innit 2 for both (a) and (b)
    O.O
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 2:25 pm

    No...not at all. The women could change seats between them. And so can the men.


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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 2:30 pm

    ahmed.. do u know the answers???
    i got 96 for (a)
    :S
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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 2:41 pm

    and i got a crazy number for (b) O.O
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 3:03 pm

    The answer for both is 1152.


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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 3:24 pm

    kkz..
    so we'll start with the order
    M1M2M3M4W1W2W3W4
    so lets look at the men..
    M1M2M3M4 (thats 1)
    M1M2M4M3 (thats 2)
    M1M3M2M4 (thats 3)
    ... etc (we'll be here for eva)
    so what we do is 4! which equals 24
    so there are 24 different ways the men can be seated in

    now lets have a look at the women...
    4! = 24
    so there are 24 different ways to seat the women..
    the Q wants all the men together AND all the women together
    so using the "and or rule" 24*24=576

    but you can have the men on the right OR the men on the left
    so again.. using the "and or rule" 576+576 = 1152

    capiche?
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 3:25 pm

    "but you can have the men on the right OR the men on the left
    so again.. using the "and or rule" 576+576 = 1152"

    ^^^That's the only step that I didn't do. Thanks!


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    Re: Permutations and Combinations

    Post by The Banker on Sun Apr 11, 2010 3:28 pm

    any time man...
    =)
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    Re: Permutations and Combinations

    Post by Ahmed on Sun Apr 11, 2010 3:32 pm

    Ill give you a "Thanks"

    Thanks=3 reps


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    Re: Permutations and Combinations

    Post by GunMan on Sun Apr 11, 2010 7:42 pm

    a) (4*3*2*1*4*3*2*1)*2 = 1152
    b) (4*4*3*3*2*2*1*1)*2 = 1152



    (a) The women are to be seated together, and the men
    are to be seated together?
    (b) They are to be seated alternately by
    gender.


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    Re: Permutations and Combinations

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