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-   -   Permutation or combination? (https://www.askmehelpdesk.com/showthread.php?t=549288)

  • Jan 30, 2011, 05:42 AM
    louis_24
    Permutation or combination?
    In how many ways can 6 individuals be seated in a round table with 6 chairs?

    a) suppose 2 persons wanted to be seated side by side, in how many ways can they do it?

    b) in how many ways can these 6 individuals arrange themselves if 2 among them refuse to sit together?

    Follow up: is the problem a permutation or a combination? Thanks for the answer!
  • Jan 30, 2011, 09:04 AM
    galactus
    Quote:

    Originally Posted by louis_24 View Post
    in how many ways can 6 individuals be seated in a round table with 6 chairs?

    The are (n-1)! Ways to arrange n people around a circular table.

    Quote:

    a) suppose 2 persons wanted to be seated side by side, in how many ways can they do it?
    Tie the two people together and pretend they are one person. There are now 5 'people' instead of 6. These can all be arranged in 4! Ways.
    But, don't forget that the two people next to each other can be arranged in 2 ways. Thus, there are ways.

    Quote:

    b) in how many ways can these 6 individuals arrange themselves if 2 among them refuse to sit together?
    Try reasoning through this one. Seat one person at a seat. You know the other person can not sit next to them. Thus, that only leaves three chairs for this person. The others can be seated in the other seats.

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