# MDM4U Permutations with some identical items 2017-09-12

We learned about how to count permutations where some items are identical (or indistinguishable). Here’s the summary:

The number of permutations of $n$ items in which $a$ are indistinguishable of one kind, $b$ are indistinguishable of another kind, and so on, is

$\frac{n!}{a!b!\ldots}$

Homework is Page 245 #3-7, 16.