Calculating a Combination
In mathematics, to calculate the combination of n things taken r at a time, we use the formula . The TI83/84 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.