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Thread: Perms and Combs help :)

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    Cadet JustRandomThings's Avatar
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    Perms and Combs help :)

    Hey everyone! Thanx in advance

    Q. Four boys and four girls sit around two concentric circles such that there are four in each circle. In how many ways can they be seated if:

    1. There are no restrictions?

    2. Three particular boys do not sit together?
    Prelimss 2017


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    Junior Member bujolover's Avatar
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    Re: Perms and Combs help :)

    Quote Originally Posted by JustRandomThings View Post
    Hey everyone! Thanx in advance

    Q. Four boys and four girls sit around two concentric circles such that there are four in each circle. In how many ways can they be seated if:

    1. There are no restrictions?
    I'm only attempting this one for now, because I can't be bothered to do the second one lol.
    Fix one person in one of the four seats of one of the circles. Then, 7*6*5 for the other three seats.
    Fix one person in one of the four seats of the other circle. Then, 3*2*1 for the other three seats.
    So answer = 7*6*5*3*2*1 = 1260.

    I might be wrong, so forgive me if I am. This is actually one of my weaker maths topics.

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