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Math Help - Normal Distribution

  1. #1
    Super Member angel.white's Avatar
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    Normal Distribution

    I found the answers to this question on this website (TUTORIAL SHEET 1 ? MA4704)

    They are very different from my answers (it's an even problem, I can't check the back of the book). Can anyone walk me through one of a or b, and one of c or d?



    Assume that X is normally distributed with a mean of 6 and a standard deviation of 3. Determine the value for x that solves each of the following.
    a) P(X>x) = 0.5
    My answer: x=6
    Other site's answer: x=7.5

    b) P(X>x) = 0.95
    My answer: x=10.95
    Other site's answer: x=8.85

    c) P(x<X<9) = 0.2
    My answer: x=7.095
    Other site's answer: x=7.08

    d) P(3<X<x) = 0.8
    My answer: x=11.235
    Other site's answer: x=7.9
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  2. #2
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    Quote Originally Posted by angel.white View Post
    I found the answers to this question on this website (TUTORIAL SHEET 1 ? MA4704)

    They are very different from my answers (it's an even problem, I can't check the back of the book). Can anyone walk me through one of a or b, and one of c or d?



    Assume that X is normally distributed with a mean of 6 and a standard deviation of 3. Determine the value for x that solves each of the following.
    a) P(X>x) = 0.5
    My answer: x=6 Mr F says: Correct.
    Other site's answer: x=7.5 Mr F says: Wrong.

    b) P(X>x) = 0.95
    My answer: x=10.95 Mr F says: Correct.
    Other site's answer: x=8.85 Mr F says: Wrong.

    c) P(x<X<9) = 0.2
    My answer: x=7.095 Mr F says: Correct.
    Other site's answer: x=7.08 Mr F says: Correct.

    The issue here is one of accuracy. A more correct answer is somewhere between these two answers.

    d) P(3<X<x) = 0.8
    My answer: x=11.235 Mr F says: Correct.
    Other site's answer: x=7.9 Mr F says: Wrong.
    ..
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  3. #3
    Super Member angel.white's Avatar
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    Thank you, Mr. F. My imprecision is because I am getting numbers off of a look up table in the Appendix of my book (is that even math?!), but it only goes to 3 digits, so I go halfway between the two closest.
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  4. #4
    Bar0n janvdl's Avatar
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    Quote Originally Posted by angel.white View Post
    Thank you, Mr. F. My imprecision is because I am getting numbers off of a look up table in the Appendix of my book (is that even math?!), but it only goes to 3 digits, so I go halfway between the two closest.
    Yes, they should be more digits. I'll see about finding my table (not like I made it, the one I just used, made by my lecturer) for you...


    Here we go, this one should be much more accurate.
    Attached Files Attached Files
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