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Thread: Probability

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    Probability

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    Hello there!!!!
    Please help me through the below probability problem:


    There are 8 red balls, 5 green balls and 3 blue balls. Three balls randomly picked up without replacement.

    i) What is the probability that the third ball would be a blue one?
    ii) What is the probability that the 2nd ball would be either green or red ball?

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    GRE-GMAT Instructor Brent Hanneson's Avatar
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    Quote Originally Posted by swack60 View Post
    Hello there!!!!
    Please help me through the below probability problem:


    There are 8 red balls, 5 green balls and 3 blue balls. Three balls randomly picked up without replacement.

    i) What is the probability that the third ball would be a blue one?
    ii) What is the probability that the 2nd ball would be either green or red ball?
    IMPORTANT: the probability that the 3rd, 4th, 5th (etc) ball is a certain color is the same as the probability that the 1st ball is a certain color. This question reminds me of my childhood, when my friends and I would sometimes "draw straws" to randomly select one person to do something. There was always one guy who wanted to select his straw last. His reasoning was that his chances of drawing the shortest piece were minimized since every person before him had a chance of drawing the short piece before it got to his turn. The truth of the matter is that each person has the same chance of selecting the shortest piece, regardless of the order in which they selected. The same applies to the original question here.

    i) P(3rd ball is blue) = P(1st ball is blue) = 3/16

    ii) P(2nd ball is green or red) = P(1st ball is green or red)
    = 1 - P(1st ball is NOT green or red)
    = 1 - P(1st ball is blue)
    = 1 - 3/16
    = 13/16

    Cheers,
    Brent

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