ABSTRACT
In combinatorics, the order of what one is trying to count sometimes matters and sometimes does not. This chapter shows when order matters it have a permutation and examines combinations, in which order does not matter. Multiplying a chain of integers that decrease from n to 1, one unit at a time, is a common event in combinatorics. So common, in fact, that a special notation has been created to represent it. The factorials wouldn’t be worthy of inclusion if the only problem they were suited for was to calculate the number of ways a group of people can arrange themselves in a grocery store checkout lane. The concept is valuable because it arises in a wide range of contexts. There are some basic functions that should be covered in any precalculus class. They are polynomials, roots, exponentials, logarithms, and trigonometric functions and their inverses.
