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Math Help - Cumulative distribution function

  1. #1
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    Cumulative distribution function

    The discrete random variable can only take the values 2, 3, 4. For these values the cumulative distribution function is defined by

    F(x)= ((x+k)^2)/25 for x= 2, 3, 4,

    where k is a positive integer.

    Find k

    I know there must be a method for this but I can't find out what it is.
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  2. #2
    Member SENTINEL4's Avatar
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    Quote Originally Posted by greghunter View Post
    The discrete random variable can only take the values 2, 3, 4. For these values the cumulative distribution function is defined by

    F(x)= ((x+k)^2)/25 for x= 2, 3, 4,

    where k is a positive integer.

    Find k

    I know there must be a method for this but I can't find out what it is.
    Well i'm not sure about that but let's see...

    As x can only take values 2,3,4 i suppose that it will be

    F(4)=\frac{(4+k)^2}{25}=1 \Rightarrow (4+k)^2=25 \Rightarrow k^2+8k-9=0
    The solutions are k=-9 and k=1 but as you say it is a positive integer we accept k=1.

    Hope i am right and helped you...
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  3. #3
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    Ok, I think I get it.
    Thanks for your help.
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