On 3 Apr 2002 08:36:47 -0800, [EMAIL PROTECTED] (david) wrote:

>u=2.7 minutes
>sigma=.6 minutes
>
>my main question is how do I get the Z value here?
>
>The question is something like this what is probability that the total
>check out time for next customers is less than 90 minutes?
>
>- I understand that Xi is (i=1,2,3) and 
>                    W = X1 + X2 . . . . and
>                    P(W<90) = P(X bar<3)
>
>BUT
>
>How does (X bar<3) = P(Z<2.74)
>
>So my main question is how does (X bar<3)=P(Z<2.74)?
>
>Could someone please explain how does this work?
>
>Thanks in advance!

check out this site:
http://psych-www.colorado.edu/~mcclella/java/normal/normz.html
It should give you a hint on how to obtain Z scores from a normal
distribution of scores.   Are you sure about the above data?   A mu of
2.7 and a standard deviation of .6 with a -90 score seems a tad off
kilter to me.  Maybe, I'm missing something here.  


.
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