# TI 83 NormalCDF function in Easy Steps

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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