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Probability

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SigGolfer 2007 Beat The GMAT Scholarship Winner! Default Avatar
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Probability Post Tue Aug 21, 2007 5:26 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    I just want to make sure that I understand this concept correctly. Please let me know if the following is correct.

    There are 3 green balls and 5 red balls in a bag.

    The probability of choosing a ball of one color, then a ball of another color would be 3/8 x 5/7 = 15/56 (around 25%)

    The probability of choosing two red balls would be 5/8 x 4/7 = 20/56 (around 35%)

    The probability of choosing two green balls would be 3/8 x 2/7 = 6/56 (around 11%)

    Is this correct? Thanks, I'm just trying to get the basics down.

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    erdnah Rising GMAT Star Default Avatar
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    Post Tue Aug 21, 2007 5:31 am
    I think the probability of choosing a ball of one color, then a ball of another color would be 3/8 x 5/7 + 5/8 x 3/7 = 15/56 + 15/56 = 30/56 = 15/28.

    This seems right, since it is the counterpart of the two other possibilities:
    two red balls would be 5/8 x 4/7 = 20/56 (around 35%)
    + two green balls would be 3/8 x 2/7 = 6/56 (around 11%)
    + probability of choosing a ball of one color, then a ball of another = 30/56
    = 56/56 = 1

    SigGolfer 2007 Beat The GMAT Scholarship Winner! Default Avatar
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    Post Tue Aug 21, 2007 5:43 am
    Thanks for your response. That's what I meant.

    First red, then green 15/56
    First green, then red 15/56

    Either red or green, then the opposite color 30/56.

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