Always start each new problem from the home screen

Sometimes we want to find the Z-score by using some given area under the curve.
The "**3:InvNorm("** option is for just such a problem.

**Example 1:** Say you want to find the Z-score for the upper 20% of a given
population. Since you want the upper 20% that means you are **at **the 80%-ile.
On the calculator we will need to go once again to the distributions menu. Go
to this screen: (below left)

**Arrow down** to choice **"3 : InvNorm
( " ** Press
(see upper right screen)

Now enter only ***1** value.

You ** must**enter the percentile of the point for which you want
the Z-score.

We will press __
____
__

**.8416212335 ** will be returned. This is the Z-score for the upper 20%.

** [ If you enter "( %-ile , mean , std.
Dev.)" the calculator **will return the actual value, not the z-score.
] *

**Example 2 : **

Say you know 50% of the area under the curve is between **z **and **-z.
**

Find** z. **

Since the **Normal Distribution function** is symmetrical it must be that
of the 50%,

25% is above the mean and 25% is below the mean.

Recall that we **must** enter **the %-ile** of the point for which we
desire the Z-score.

The mean is in the middle of the curve so its %-ile is 50% and since 25% is above the mean then we want the Z-score for the 75%-ile. ( 50% + 25%)

We see that **z = .674 **