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Math Help - Probability for a certain event

  1. #1
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    Probability for a certain event

    Todays really not my day, I should know this but I'm just too unsure:

    Let's say we got a chest with 30 balls in there, 25 black and 5 golden.
    I want to find out the probability to get at least 1 golden ball, having 5 tries and not being allowed to put the balls back in there once I get them out.

    I do know that its

    1 - P(no golden balls in 5 tries)

    but I'm having trouble remembering how to get my P

    is it 5/30+5/29+...
    or 1/25+1/24+...
    or maybe 1/30+1/29+...

    or even something completely different?

    Thanks for your time
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  2. #2
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    Re: Probability for a certain event

    Quote Originally Posted by MuhTheKuh View Post
    Todays really not my day, I should know this but I'm just too unsure:

    Let's say we got a chest with 30 balls in there, 25 black and 5 golden.
    I want to find out the probability to get at least 1 golden ball, having 5 tries and not being allowed to put the balls back in there once I get them out.

    I do know that its

    1 - P(no golden balls in 5 tries)

    but I'm having trouble remembering how to get my P

    is it 5/30+5/29+...
    or 1/25+1/24+...
    or maybe 1/30+1/29+...

    or even something completely different?

    Thanks for your time
    Pr(at least one) = 1 - Pr(none) and Pr(none) = (25/30)(24/29) ....(21/26)
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