Area Under The Curve

[Guzzlr]

Hello all...
I have a simple distribution, lets say: N(100,10). Is there an excel function to find area under the curve, so I can find my Z value? For that matter, is there an excel function which will simply give me the Z value with mean of 100, and standard deviation of 10? I know (and have used) descriptive statistics in the add-ins, but I'm not seeing how to find the area for finding Z.
Thanks for the help
Charles

 

[xenou]

NORMDIST gives you the area under a curve. For a standard normal curve the mean is 0 and the standard deviation is 1.

A z score simply assumes that the mean is 0 and the standard deviation is 1. You convert a value in a standard curve to a value in a standard normal curve (z score) with:
<img src="http://wise.cgu.edu/images/z_eq.JPG" />

 

[Guzzlr]

right...unfortunately, I do not have a value of X. All I have is mew. and standard deviation. I'm trying to find area under the curve with just these two numbers (100 , 10). with out having to pull the calculus books out.
Thanks
Charles

 

[xenou]

I may be wrong but without a value for x, you don't have enough information. Though by definition the area under a normal curve is 1; a z-score where x is equal to the mean is always 0; and the area under the curve at the mean is 0.50.

In other words, mu and sigma define the curve, but don't define any point along the curve. So there's no z-score with only that much information - just a curve containing an infinite number of possible points, each of which would have a z-score.

 

[Guzzlr]

The problem was a screwy worded problem. The standard deviation is defined in this case as "Standard Deviation over Lead Time". And, Safety Stock is defined as a one month supply (with an annual demand of 300). Therefore:
Safety Stock = Z * (Standard Deviation * Lead Time)
So, 25=Z *10
So, Z=2.5, which gives an area under the curve in the Z-Tables of .99379, or 99.4%.
What was throwing me was the way the problem was worded, sorry for wasting your time.
Thanks
Charles