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Math Help - Beta Distribution

  1. #1
    Newbie
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    Dec 2009
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    Beta Distribution

    Hi,

    I'm trying to work out P(Y≥0.9) for Y~Beta(4,1).
    I did P(Y≥0.9) = 1- P(Y≤0.9)
    = 1 - (5-1)!/(4-1)! * (0.9^3) * (1-0.9)^0
    = 1 - 2.916 = -1.916

    But this is obviously wrong! I can't see where i have gone wrong.

    Thanks for any help.
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  2. #2
    Senior Member Danneedshelp's Avatar
    Joined
    Apr 2009
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    Quote Originally Posted by blacksheep View Post
    Hi,

    I'm trying to work out P(Y≥0.9) for Y~Beta(4,1).
    I did P(Y≥0.9) = 1- P(Y≤0.9)
    = 1 - (5-1)!/(4-1)! * (0.9^3) * (1-0.9)^0
    = 1 - 2.916 = -1.916

    But this is obviously wrong! I can't see where i have gone wrong.

    Thanks for any help.
    I am not sure what you did, but given Y~Beta(4,1), I would use the Beta pdf of Y to solve.

    P(Y\geq\\0.9)=\frac{\Gamma(4+1)}{\Gamma(4)\Gamma(1  )}\int_{0.9}^{1}y^{4-1}(1-y)^{1-1}dy<br />
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