Finding Z Score of a given Area-HELP!!!

[peggyskold]

This problem asks me to find the Z Score that corresponds to an area of 0.8925--it says that the row value is 1.2 and the column value is 0.04 so the Z Score is 1.24??? How do they come up with 1.2 and 0.04 from 0.8925??? The book does not explain how and I certainly don't see it? Anyone? Thanks
Peggy

 

[galactus]

Look up .8925 in the body of the z table and we see the corresponding value is 1.24

How do they come up with these values?. It is a complicated integral. That is why we use a z-table where they are already figured out for us.

The .8925 is 89.25% of the area under the normal curve. The 1.24 means it is 1.24 standard deviations above the mean.

If you are interested, the integral these are derived from is:

\(\displaystyle \frac{1}{\sqrt{2\pi}}\int_{-\infty}^{z}e^{\frac{-t^{2}}{2}}dt\)

If you use a calculator or computer and plug in z=1.24 in the above integral, you will get .8925 or very close.

 

[peggyskold]

Got it now. All I needed to read was "look for .8925 in the BODY of the table and find the corresponding Z score....It was not worded that way and I thought I was missing a step--I certainly am capable of reading a table and I just didn't realize that all they were doing was telling me to read the table going from the body out as opposed to the columns in--just more of reading the table.....So now that I spent all of this time on something so simple, I thank you for simplifying that for me. Thanks
Peggy