**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 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 10,** RIGHT ARROW** and then type **7 **and press
**ENTER.** The results are shown below.

Thus, =
**120.**

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