# Probabilities of z-scores

• Nov 20th 2006, 11:13 AM
GoneFishing
Probabilities of z-scores
Does anyone have a link to the chart that you use to find the probabilities of z-scores? Mine is not in my book.

A question like:

P(-2.02<z<0.58)

How do you go about handling that?
• Nov 20th 2006, 11:38 AM
ThePerfectHacker
Quote:

Originally Posted by GoneFishing
Does anyone have a link to the chart that you use to find the probabilities of z-scores? Mine is not in my book.

A question like:

P(-2.02<z<0.58)

How do you go about handling that?

Firstly the chart does not work for all values.
You need to simplify that.
\$\displaystyle P(-2.02<z<.58)=P(-2.02<z<0)+P(0<z<.58)\$
Now,
\$\displaystyle P(0<z<.58)\$ you can find by chart.
And,
\$\displaystyle P(-2.02<z<0)=P(0<z<2.02)\$ because the normal curve is symetrrical. And then use the chart.
Heri
• Nov 21st 2006, 07:24 AM
GoneFishing
So when you get those decimals, do you add them together or subtract them to get the final answer?
• Nov 21st 2006, 07:26 AM
ThePerfectHacker
Quote:

Originally Posted by GoneFishing
So when you get those decimals, do you add them together or subtract them to get the final answer?

Of course.
• Nov 21st 2006, 07:29 AM
GoneFishing
Add or subtract? I'm struggling here. lol The concept of the greater than or less than sign is bothering me, too.

If you have this:

P (z.>2.18) and P (z<1.77)...what is the difference in the final answer?
• Nov 21st 2006, 08:33 AM
CaptainBlack
See here

RonL