# 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)*