# 3: Combinatorics

- Page ID
- 3129

- 3.1: Permutations
- Many problems in probability theory require that we count the number of ways that a particular event can occur. For this, we study the topics of permutations and combinations. We consider permutations in this section and combinations in the next section.

- 3.3: Card Shuffling
- Given a deck of n cards, how many times must we shuffle it to make it “random"? Of course, the answer depends upon the method of shuffling which is used and what we mean by “random."

Thumbnail: Pascal's triangle contains the values from the binomial expansion where each number is the sum of the two numbers directly above it. (Public Domain; __Hersfold__ via Wikipedia)