Solution 11933: Calculating Two-Variable Statistics on the TI-83 Plus Family of Graphing Calculators.
How do I calculate two-variable statistics on the TI-83 Plus family of graphing calculators?
Follow the example below to calculate two-variable statistics:
Data for this example:
1) Press [STAT]  to access the STAT list edirtor.
2) Enter the data in the L1 and L2 lists, making sure to press [ENTER] after each entry.
3) Press [2nd] [MODE] to QUIT and return to the home screen.
Calculating the two-variable statistics:
1) Press [STAT], arrow right to highlight the CALC menu and press  to select the 2-Var Stats function.
2) Press [2nd]  [,] [2nd]  to input L1,L2.
3) Press [ENTER] and the two-variable statistics data will be displayed. The [up arrow] and [down arrow] keys can be used to scroll through the data.
Please see the TI-83 Plus Family guidebooks for additional information.