Statistics How To

How to Use the TI-89 to calculate combinations

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The TI-89 Titanium graphing calculator is a hand held calculator that helps you calculate many statistics and probability problems in seconds. A permutation problem is one where a certain number of items are selected in order and that order doesn’t matter. While doing this by hand is cumbersome (the equation you use involves factorials: n!(n – r)!), the calculator can figure it out at the press of a button.

Sample problem: If there are 5 people, Barb, Sue, Jan, Jim, and Rob, and only three will be chosen for the new Parent Teacher Association, how many combinations are possible for the committee?

Step 1: Press the Home screen on the calculator.

Step 2: Press the Catalog key.

Step 3: Press Alpha 6. This selects the letter “n” and brings you to the “n”s in the list. If it doesn’t, try pressing Alpha 6 again.

Step 4: Find nCr(. Press Enter.

Step 5: Press 5. This is the number of possible people, or n.

Step 6: Press , then 3. This is the number of people we need to choose, or r.

Step 7: Press ). The entry on your calculator should now read nCr(5,3). Press Enter. This returns you result. There are 10 possible ways this committee can be chosen.

Tip: Instead of hitting the Alpha and 6 keys, use the scroll button to scroll through the menu.
Tip: Want to check your answer? Use our free, online combinations calculator and permutations calculator to check your work.

Lost your guidebook? You can download a new one from the TI website here.

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