Chapter 11 - Counting Methods and Probability Theory - 11.2 Permutations - Concept and Vocabulary Check - Page 700: 3

$\displaystyle \frac{n!}{p!q!}$

See: Permutations of Duplicate Items, page 699. The number of permutations of $n$ items, where $p$ items are identical, $q$ items are identical, $r$ items are identical, and so on, is $\displaystyle \frac{n!}{p!q!r!\ldots}$ ------------------ Fill the blank with $\displaystyle \frac{n!}{p!q!}$