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Math Help - Standard normal

  1. #1
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    Standard normal

    Standard normal-phpxwrdut.png

    Standard normal-screen-shot-2012-10-29-11.12.15-am.png

    Work done so far....
    If X ~ N(22,4), z = (x - 22)/sqrt(4) ~ N(0,1) Thus, P(20 <= X <= 21) = P((22-20)/2 <= z <= (22-21)/2) = P(1<= z <= 0.5) = P(z <= 1) - P(Z <= 0.5) Now, we use the table above. P(z <= 1) - P(Z <= 0.5) = 0.8413-0.6915=0.1463

    Is it correct?
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Standard normal

    Check your arithmetic at the very end, using numeric integration (assuming \mu=22 and \sigma^2=4 I'm not familiar with the notation given) I find:

    P(20<X<21)\approx0.14988228

    and using the table I have, I get 0.1498
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