Originally Posted by

**Coukapecker** Hi,

Me and my G12 teacher are having a debate about a question he marked wrong on one of my tests.

The question was true or false:

I put false, reason being it truly isn't undefined. Z scores can continue on to positive/negative infinity, all of which are defined. Z scores > 4 perhaps are **negligable**, but most definitely not undefined.

The reason my teacher says it is undefined is because of the way we go about calculating the probability using the z scores. Instead of using the antiderivative (the accurate way to determine percentages from a z score, i would think), we use a table that has z scores and their corrosponding percentages listed. We simply round to the nearest percent.

Since the table we use only goes to a min of -4 and a max of +4, he says that all scores above and below that range are undefined.

The class im taking is a financial math class, which is why we use a simple table rather than figuring out the antiderivative of the normal distribution curve. I hope to show my teacher that the way the table he uses was generated was using calculus, and more importantly z scores above and below -4/+4 are most definitely not undefined.

The problem I've encountered, is I'm a bit rusty since my calculus classes a few years ago, and I can't find the equation of normally distributed data :\.

Through a bit of searching, I found that the normal distribution is a form of the gaussian function.

I got the equation $\displaystyle f(x)=e^(-x^2)$, but the problem is the total area under the curve doesn't come to 1, how can i mold it so it does come to 1, so that when I find the area under a certain section of the curve it will be a percent in decimal form?

any help would be appriciated,

thanks,

Coukapecker