Calculating a Combination

In mathematics, to calculate the combination of n things taken r at a time, we use the formula . The TI-83/84 has this formula already built in.

To calculate , on the home screen first press 10, then press the MATH key. Next press the RIGHT ARROW key three times so that PRB is highlighted. Press 3 to select the combination formula. Next type 7 and press ENTER. The results are shown below.



Thus, = 120.

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