 # Critical Z Value TI 83: Easy Steps for the InvNorm Function

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## Critical z value TI 83 A critical value in a hypothesis test separates the region where the hypothesis will be rejected from the region where the hypothesis will not be rejected. You could use the equation above to find the z-score; with a little arithmetic, you can look up a critical value in a z-table, or you can use the InvNorm function on the TI-83 graphing calculator.

Find more help for the TI 83 and statistics by visiting the main TI 83 for statistics menu.

## Critical z value TI 83: Steps

InvNorm can be used in a couple of different ways. The first problem shows you how to find a critical value (a z-score) for a given alpha level for example, α=0.05. The second problem shows you how to use InvNorm find a specific score for data with a normal distribution.

Sample Problem #1: Find the critical z value for α=0.05.

Watch the video or read the steps below:

Step 1: Press 2nd VARS 3. This displays InvNorm( on the home screen.

Step 2: Type one of the following:
0.05 (for a one tailed test)
0.05/2 (for a two tailed test).
Not sure? See: One Tailed Test or Two.

Step 3: Press the ) button.

Step 4: Press Enter.

• -1.64 is the z-score for the left tail.
• 1.64 is the z-score for the right tail (because the normal distribution is symmetrical).
• -1.96 is the area in the left tail for a two tailed test
• 1.96 is the area in the right tail for a two tailed test (because the normal distribution is symmetrical).

Sample Problem #2: An end of semester exam is normally distributed with a mean of 85 and a standard deviation of 10. Find the score at the 90th percentile with the InvNorm function.

Step 1: Press 2nd VARS 3. This displays InvNorm( on the home screen.

Step 2: Type .90,85,10.

Step 3: Press the ) button.

Step 4: Press ENTER. This returns 97.82. That means that 90% of students will have scores below 97.82.

That’s it! Like the explanation?

That’s how to find a Critical z value TI 83!

Tip: The first entry on InvNorm should be a number between 0 and 1.