At Capitan High School, we use TI84 Silver Edition graphing calculators in our math classes. These have a lot of built in statistical functions that make our job much easier. All the instructions below were done specifically for a TI84 graphing calculator, but the instructions will also work for a TI82 or TI83. If you are using a TI89 please check with your users manual.
More recently, we have upgraded to the TINspire graphing calculators and even have two Nspire color calculators.
I strongly suggest that you visit the education.ti.com site for detailed tutorials on how to use your calculator fully.
The following steps, in order, are required to use a graphing calculator in solving problems in statistics:
For the instructions below, (2nd) means to use the second function button (top left, just below the Y= button) followed by a second function, listed in blue above one of the regular buttons on your TI84 graphing calculator.
Before starting, you need to be sure to clear any previous data out of your calculuator. There are two choices for how to do this. I usually just clear the whole memory (RAM), but you can also clear one list at a time.
To clear everything 
To clear only one list 

(2nd) MEM
7: Reset 1: All RAM 2: Reset 
MEM is above the + key 
STAT
4: ClrList (2nd) LIST pick list you want 
LIST is above the STAT key 
The TI graphing calculuators use LIST to enter data for use in statistics and other applications. Once the data is in a list, it can be graphed or used to do calculuations.
To enter data 

STAT
1: Edit Enter data into one of the lists 
use ENTER after you add each number to your list 
For use in all examples on this page, practice by entering data into List 1 (L1). Use the following data: 5, 9, 8, 4, 2, 7, 6, 1, 9, 3, 5
Use the up and down arrows to move to the last number in your list. If you did the example correctly, at the bottom of the screen it will say:
L1(11)=5
This means that the eleventh number in list L1 is 5.
This section explains how to use the data you have entered into a list to do some of the standard calculuations in statistics. To follow along with the examples, you should have done steps 1 and 2, entering the sample data found in step 2.
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