Probability and Statistics > TI 83 > TI 83 NormalCDF

## TI 83 NormalCDF: Overview

The **TI 83 graphing calculator** can help you figure out **normal distribution probabilities** with the normalcdf function located in the VARS section of the calculator.

Normalcdf is the normal (Gaussian) cumulative distribution function on the TI 83 calculator. If a random variable is normally distributed, you can use the normalcdf command to find the probability that the variable will fall into a certain interval that you supply.

The format for normalcdf is: **normalcdf(lower bound, upper bound, mean, standard deviation)**. If you have a standard normal distribution (where the mean is 0 and the standard deviation is 1) you can leave the last two variables out, as those are the default settings on the calculator.

## TI 83 NormalCDF: Steps

Watch the video or read the steps below:

**Sample problem**: A group of students taking end of semester statistics exams at a certain college have a mean score of 75 and a standard deviation of 5 points. What is the probability that a given student will score between 90 and 100 points? Use the NormalCDF function.

**Step 1:** Press the **2nd **key and then press **VARS **then **2 **to get “normalcdf.”

**Step 2:** Enter the following numbers into the screen:

90 for the lower bound, followed by a comma, then 100 for the upper bound, followed by another comma.

**Step 3: Press ****75** (for the mean), followed by a comma and then **5 **(for the standard deviation).

**Step 4:** Close the argument list with a “)”. (Your display should now read **normalcdf(90, 100, 75, 5)**.) Now press **ENTER**. The calculator returns the probability, which in this case is 0.00135, or **.135%** (to three decimal places).

That’s how to use the TI 83 NormalCDF function!

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In case anyone reads this, 0.00135 is equal to 0.135%, not 1.35%.

You’re completely right. I fixed the typo — thanks for spotting it!

Stephanie

Why does it say “(to two decimal places)” after .135%? I thought .135% is three decimal places?

Whoops! You are completely right. It’s three decimal places. Thanks for catching that typo.