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Math Help - lost with counting:(

  1. #1
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    lost with counting:(

    a company orders supplies from 10 distributor and wishes to place 7 orders. what is the probability that
    a. all the orders go to different distributors
    b. distributor 1 gets 2 orders and distributor 2 gets 3 orders
    c. distributor 1,2,3 gets 2,3,1 orders respectively?

    sorry, im really bad at probability...not sure how to approach such questions..
    thanks!
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  2. #2
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    Quote Originally Posted by stressedout View Post
    a company orders supplies from 10 distributor and wishes to place 7 orders. what is the probability that
    a. all the orders go to different distributors
    b. distributor 1 gets 2 orders and distributor 2 gets 3 orders
    c. distributor 1,2,3 gets 2,3,1 orders respectively?
    This question is about counting and not probability.
    Some aspects of the question bother me: Are we to assume that the orders are distinct?
    If so there 10^7 ways to place the orders.
    So the answer to part a) is P(10,7)=\frac{10!}{(10-7)!}

    b) \binom{7}{2}\binom{5}{3} 8^2

    What do you think about part c)?
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  3. #3
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    Quote Originally Posted by Plato View Post
    This question is about counting and not probability.
    Some aspects of the question bother me: Are we to assume that the orders are distinct?
    If so there 10^7 ways to place the orders.
    So the answer to part a) is P(10,7)=\frac{10!}{(10-7)!}

    b) \binom{7}{2}\binom{5}{3} 8^2

    What do you think about part c)?
    the answers from my text are
    0.0605, 0.001344 and 0.00029 though..
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  4. #4
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    Quote Originally Posted by stressedout View Post
    the answers from my text are
    0.0605, 0.001344 and 0.00029 though..
    Am I correct in inferring from that cryptic ‘though’ that you did not work out the suggested answered? Had you put just a little effort into what is after all your assignment, you would have seen that the answers given by the text are exactly the same as those I posted.
    Until you show some effort on you part, do not expect any more help from me.
    You can start by working on part c). You know the correct answer, so how is gotten?
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  5. #5
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    im so sorry.

    for part (a) i punched in 10! / 3! = 604800. i assumed that when you meant that the answer for part (a) is as follows...that it was the answer. i didnt know that i have to divide it by 10^7. so so sorry...

    this also happened for the second part of the question.

    for part (c) (7 choose 2 ) x ( 5 choose 3) x( 2 choose 1 ) x 7 / 10^7
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