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Math Help - How can you calculate percentiles from a cdf?

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    How can you calculate percentiles from a cdf?

    I'm having some trouble understanding how to calculate the percentile from a cdf, i realize that a percentile ( ie. percentile .95) is the value in which 95% of all the probabilities contained within the function fall below - but how do you calculate that value from a function?

    the fuction i was given is : ky(1-y) where 0>y>1 , btw this is my first post so i didnt know how to do a greater than or equal sign.. but that's what it's supposed to be! thanks

    And if Mr.Fantastic is reading this, you've already saved my life a couple times. So thank you
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    Quote Originally Posted by Jobocop View Post
    I'm having some trouble understanding how to calculate the percentile from a cdf, i realize that a percentile ( ie. percentile .95) is the value in which 95% of all the probabilities contained within the function fall below - but how do you calculate that value from a function?

    the fuction i was given is : ky(1-y) where 0>y>1 , btw this is my first post so i didnt know how to do a greater than or equal sign.. but that's what it's supposed to be! thanks

    And if Mr.Fantastic is reading this, you've already saved my life a couple times. So thank you
    I save many lives. Every day.

    Is f(y) = ky(1-y) where 0<y<1 the pdf?

    If so, then first you must get the value of k by solving \int_0^1 k y(1 - y) \, dy = 1.

    Then the 95th percentile is the value of a such that \int_0^a k y(1 - y) \, dy = 0.95.
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