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Math Help - true???

  1. #1
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    true???

    the comulative distribution :
    given by >>>>
    F(x)=
    0 x<=0
    x\8 0<=x<4
    x^2\16 2<=x<4
    1 x>=4


    find >>>>>>>>>
    1-mean of (-2-3x)
    2-p(1<x<3)
    my solutions
    1-mean = -41\4
    2- p(1<x<3)= 1\4
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by flower3 View Post
    the comulative distribution :


    given by >>>>
    F(x)=
    0 x<=0
    x\8 0<=x<4
    x^2\16 2<=x<4
    1 x>=4


    find >>>>>>>>>
    1-mean of (-2-3x)
    2-p(1<x<3)
    my solutions
    1-mean = -41\4

    2- p(1<x<3)= 1\4
    The mean cannot be negative, the probability that x is less than or equal 0 is 0.

    You need to find the density f(x)=F'(x) (you don't need to worry about this being undefined at a finite number of points) first then the mean will be:

    \int_{-\infty}^{\infty} x f(x)\ dx

    p(1<x<3)=F(3)-F(1)=3/8-1/6=1/4

    RonL
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  3. #3
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    the probability impossible equal negative since:

    0<=p(x)<=1

    but the mean maybe negative or positive>>>>
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by flower3 View Post
    the probability impossible equal negative since:

    0<=p(x)<=1

    but the mean maybe negative or positive>>>>
    Look at the definition of mean, if p(x)=0 far all x<0, then the integrand of defining integral for the mean is never negative, so the integral is positive.

    If the probability that a rv is negative is zero, the mean is of necessity positive (or zero).

    RonL
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  5. #5
    Flow Master
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    Quote Originally Posted by flower3 View Post
    the comulative distribution :


    given by >>>>
    F(x)=
    0 x<=0
    x\8 0<=x<4 Mr F says: That 4 should be a 2.
    x^2\16 2<=x<4
    1 x>=4


    find >>>>>>>>>
    1-mean of (-2-3x)
    2-p(1<x<3)
    my solutions
    1-mean = -41\4

    2- p(1<x<3)= 1\4
    The hard evidence supporting CaptainB (not that he needs supporting since his comments are bombproof) is that the mean (assuming my correction is correct) is 31/12.
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  6. #6
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    yes
    mr fantasticyour saying is true(2 not 4)

    i think the truth is :


    1-mean = -39\4

    2- p(1<x<3)= 7\16


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  7. #7
    Grand Panjandrum
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    Quote Originally Posted by CaptainBlack View Post
    Look at the definition of mean, if p(x)=0 far all x<0, then the integrand of defining integral for the mean is never negative, so the integral is positive.

    If the probability that a rv is negative is zero, the mean is of necessity positive (or zero).

    RonL
    Ahh.. I see my confusion I was misreading the question you want the mean of -2-3x which is of course negative since the mean of x is positive, and so is equal to -2-3\bar{x}

    RonL
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  8. #8
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    Quote Originally Posted by CaptainBlack View Post
    Ahh.. I see my confusion I was misreading the question you want the mean of -2-3x which is of course negative since the mean of x is positive, and so is equal to -2-3\bar{x}

    RonL
    Don't worry
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