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Math Help - Standard normal distribution

  1. #1
    Yan
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    can any one help me out!!! -the answer still not right!!

    If Z is a random variable having the standard normal distribution,find

    A) P (Z>=-0.79);
    B) P (-1.90>=Z>=0.44).
    Last edited by mr fantastic; February 22nd 2009 at 10:34 PM. Reason: Restored question deleted by OP
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  2. #2
    Moo
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    Hello,
    Quote Originally Posted by Yan View Post
    If Z is a random variable having the standard normal distribution, find
    A) P (Z>=-0.79);
    B) P (-1.90>=Z>=0.44).
    Here are general rules for the standard normal distribution (and it will look very logical if you look at a z-table : http://www.science.mcmaster.ca/psych...e/z-table2.jpg)

    define p(.) as the black area. it's defined for positive values.

    If a>0
    P(Z>a)=0.5-p(a)
    P(Z<a)=1-P(Z>a)=0.5+p(a)

    If a<0
    P(Z<a)=P(Z>-a)=0.5-p(-a)
    P(Z>a)=P(Z<-a)=0.5+p(-a)

    P(a<Z<b)=P(Z<b)-P(Z<a)

    and that's all ^^
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  3. #3
    Yan
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    Quote Originally Posted by Moo View Post
    Hello,

    Here are general rules for the standard normal distribution (and it will look very logical if you look at a z-table : http://www.science.mcmaster.ca/psych...e/z-table2.jpg)

    define p(.) as the black area. it's defined for positive values.

    If a>0
    P(Z>a)=0.5-p(a)
    P(Z<a)=1-P(Z>a)=0.5+p(a)

    If a<0
    P(Z<a)=P(Z>-a)=0.5-p(-a)
    P(Z>a)=P(Z<-a)=0.5+p(-a)

    P(a<Z<b)=P(Z<b)-P(Z<a)

    and that's all ^^
    but i still don't know how to do the (b) part?
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  4. #4
    Moo
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    Quote Originally Posted by Yan View Post
    but i still don't know how to do the (b) part?
    0, since -1.9 can't be > 0.44
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  5. #5
    Yan
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    Quote Originally Posted by Moo View Post
    0, since -1.9 can't be > 0.44
    but, in my solution sheet, the answer is 0.6134
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  6. #6
    MHF Contributor matheagle's Avatar
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    Your inequalities are backwards.
    It's just F(.44)-F(-1.9), where you look up those values in st normal table.
    And I bet you meant...
    P(-1.90\le Z \le 0.44).
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