TI83/84: DIY Inverse chi-square program

The inverse chi square function isn’t pre-loaded on TI-83 and TI-84 calculators. Inverse chi square returns a critical value we use in hypothesis tests and confidence intervals for population variance.

Here is a simple 3-line program for inverse chi square you can enter in your calculator.

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Go to PRGM, NEW, 1. Create New
At the Name = prompt, the cursor is already in alpha mode, type a short name. I used INVCHI.
ENTER

And we’re ready to write the program!

: Input “AREA RIGHT:”,A
: Input “DF:”,D
: Disp solve(1-X2cdf(0,X,D)-A,X,0)
:

Click 2nd MODE to exit the program.

Now go to PGRM, EXEC, and you’ll see your INVCHI program in the list. Click to select it.
prgmINVCHI is pasted to the home screen. Click ENTER to activate it.

You should see the AREA RIGHT prompt.

Test it with the following (press ENTER after each entry):
AREA RIGHT: .05
DF: 13

It may take a few seconds to find the solution. Check answer: 22.362

Press ENTER again to find another chi square critical value.

Reload the program any time in PRGM, EXEC.

Tips for building and using the program:
- The colon adds itself to the start of each line automatically.
- If you need to exit out of a menu while programming, use 2nd MODE.
- Your work saves automatically. Go back to PRGM, EDIT, INVCHI to continue working.
- Input and Disp commands are in PRGM, I/O.  Solve (or Solver) is in MATH. X2cdf is in 2nd VARS.
- For AREA RIGHT, always enter area to the right of chi square.

• #education
• #ti_83
• #ti_84
• #inverse_chi_square
• #chi_square_critical_value
• #business_statistics
• #busstat
• #hypothesis_test
• #population_variance