Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 11 - Counting Methods and Probability Theory - 11.3 Combinations - Concept and Vocabulary Check - Page 707: 2

Answer

$r!$

Work Step by Step

Comparing ${}_{n}P_{r}=\displaystyle \frac{n!}{(n-r)!}\quad$ and $\quad {}_{n}C_{r}=\displaystyle \frac{n!}{(n-r)!r!}$, the extra factor in the denominator of ${}_{n}C_{r}$ is $r!$
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