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Math Help - permutation problem 1

  1. #1
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    permutation problem 1

    hey guys, need some help with this problem. this is one of four permutation problems that our teacher gave us to solve but haven't really figured it out, plus i was sick so i missed the lecture..

    1) Suppose a student lives in a dormitory.

    A: In the common area there are 20 books and 24 magazines. How many ways can we choose either? and having chosen one of each, how many ways can we choose another book and magazine?

    B: If there are 8 outside doors in the dorm, how many ways can a student enter one and leave by b1) a different door and b2) any door?

    thanks for the help. we've been given all the basic formula for permutations but I'm at a loss at how to apply them still.
    Last edited by Jhevon; April 26th 2009 at 01:30 PM.
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  2. #2
    Member SengNee's Avatar
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    Pangkor Island, Perak, Malaysia.
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    Quote Originally Posted by wheresthecake View Post
    hey guys, need some help with this problem. this is one of four permutation problems that our teacher gave us to solve but haven't really figured it out, plus i was sick so i missed the lecture..

    1) Suppose a student lives in a dormitory.

    A: In the common area there are 20 books and 24 magazines. How many ways can we choose either? and having chosen one of each, how many ways can we choose another book and magazine?

    B: If there are 8 outside doors in the dorm, how many ways can a student enter one and leave by b1) a different door and b2) any door?

    thanks for the help. we've been given all the basic formula for permutations but I'm at a loss at how to apply them still.
    A: My english is poor, I can't see the question clearly.

    B:
    1)
    Enter: 8 doors
    Exit: 7 doors(cannot use the previous door)
    ^8P_1 \cdot ^7P_11
    or
    ^8C_1 \cdot ^7C_1
    or
    8 times 7

    2)
    Enter: 8 doors
    Exit: 8 doors(can use the previous door)
    ^8P_1 \cdot ^8P_11
    or
    ^8C_1 \cdot ^8C_1
    or
    8 times 8
    or
    8^2
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