Probability and Statistics > TI 83 > TI 83 NormalCDF + YI 84

## TI 83 NormalCDF / TI 84: Overview

The **TI 83 and TI 84 graphing calculators** can help you figure out **normal distribution probabilities** with the normalcdf function.

Normalcdf is the normal (Gaussian) cumulative distribution function on the TI 83/TI 84 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.

## Where is NormalCDF on the Calculator?

On both the TI 84 and TI 83, NormCDF is in the same place:

- Press the 2nd key.
- Press VARS .
- Scroll to option 2—or just press “2”— for “normalcdf.”

## Format

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 & TI 84: Steps

Watch the video or read the steps below. Although I’m using a TI 83 here, the TI 84 steps are identical:

**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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