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Math Help - Probability Test

  1. #1
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    Probability Test

    Gah i posted 2 questions about my test earlier, cud u pls check it
    Last edited by andrew2322; May 10th 2008 at 08:51 PM.
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  2. #2
    Moo
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    Hello,

    Questions 1, 2 and 3 are ok.

    Question 4 :

    a.) The first marble picked is black and the second is red: 5/36
    I don't see any black marble :/

    b.) Obtaining 2 white marbles: 1/16
    Ok.
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  3. #3
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    sorry

    Find One Lol
    Last edited by andrew2322; May 10th 2008 at 08:52 PM.
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  4. #4
    Moo
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    Good job !
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  5. #5
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    Talking hey

    booo
    Last edited by andrew2322; May 10th 2008 at 08:51 PM.
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  6. #6
    Moo
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    Yes ^^

    Unless I made mistakes too, but all the reasoning is correct !
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  7. #7
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    hey

    haha i doubt two people can make the exact same mistake
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  8. #8
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    So far #1 and #2 are correct, but #3 has an error...

    3.) A red and a black die labelled 1 - 6 are thrown simultaneously, find the probability of:

    a.) A number less than 5 on the red die: 2/3
    b.) A number less than 5 on the red die but a totla of 10 altogether: 1/36
    c.) Both die adding to 10: 1/12
    a) is correct

    given that, b) should be equal to \frac{2}{3}*\frac{1}{6} = \frac{1}{9}

    c) is correct, three possibilities out of thirty-six

    4.) There is 3 white marbles, 4 blue marbles and 5 red marbles in a bag. Find the probabilty of if marbles are picked WITH REPLACEMENT:

    a.) The first marble picked is black and the second is red: 5/36
    b.) Obtaining 2 white marbles: 1/16
    a) 0, there are no black marbles
    b) \frac{3}{12}^2 = \frac{9}{144}, Remember, the white marble is replaced by another white marble.

    #5, #6 and #7 are all correct

    Note: Best way to solve #7 is by using a Venn diagram
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  9. #9
    Moo
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    Quote Originally Posted by colby2152 View Post
    a) 0, there are no black marbles
    He said it was blue

    b) \frac{3}{12}^2 = \frac{9}{144}, Remember, the white marble is replaced by another white marble.
    The probability to get a white marble is 3/12=1/4
    Since there is replacement, the probability to get 2 marbles will be the product of the probabilities of getting 1 marble, that is to say 1/4=1/16, isn't it ?
    Actually, 9/144 is 1/16...
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  10. #10
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    Quote Originally Posted by colby2152 View Post
    given that, b) should be equal to \frac{2}{3}*\frac{1}{6} = \frac{1}{9}
    The thing is that the red dice has to be < 5, so 1 2 3 or 4.
    Since the total has to be 10, the only possibility is that the red dice is 4 and the blue dice is 6 -> 1/36
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  11. #11
    GAMMA Mathematics
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    Quote Originally Posted by Moo View Post
    The probability to get a white marble is 3/12=1/4
    Since there is replacement, the probability to get 2 marbles will be the product of the probabilities of getting 1 marble, that is to say 1/4=1/16, isn't it ?
    Actually, 9/144 is 1/16...
    Yep, \frac{9}{144} = \frac{1}{16}

    Quote Originally Posted by Moo View Post
    The thing is that the red dice has to be < 5, so 1 2 3 or 4.
    Since the total has to be 10, the only possibility is that the red dice is 4 and the blue dice is 6 -> 1/36
    Both adding to 10 is the event of a 6 on one die and a 4 on another. This probability is 1/36. I read the question wrong.
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