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Math Help - Permutations and Combinations

  1. #1
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    Red face Permutations and Combinations

    I'm currently having a bit of trouble with some questions, this one in particular. Everytime I try and do it I end up doing some sort of statistic probability, which is not what I need. The question is:

    Suppose that a die is tossed ten times and the sequence of upturned numbers is recorded in order

    a) How many outcomes are there?
    b) How many outcomes are there exactly 3 fours?
    c) How many outcomes are there at most 3 fours?

    What I have done so far is figured out that there would be 6^10 different possible outcomes, but apart from that I keep going in a loop for b and c. Any help would be appreciated, or any pointers into what I should be looking at doing.
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  2. #2
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    Quote Originally Posted by Darky001 View Post
    Suppose that a die is tossed ten times and the sequence of upturned numbers is recorded in order
    b) How many outcomes are there exactly 3 fours?
    c) How many outcomes are there at most 3 fours?
    b) You have ten positions in which to put the fours, choose three of them:
    Combin(10,3)(5^7). In the other seven places put any one of five other numbers.

    c) Sum{k=0 to k=3}Combin(10,k)(5^{10-k}).
    Last edited by Plato; May 14th 2007 at 01:29 PM.
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  3. #3
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    Ahh thankyou!
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