College Algebra Chapter 1/Section 1 Review We begin our College Algebra journey with a review of the basics according to the author of the textbook. Working with sets. There are two methods for denoting sets: Roster Method Set-Builder Notation Let O = set of odd digits Roster Method O = {1, 3, 5, 7, 9 } I never understood 1 as an odd digit. You say? Set-Builder Notation O = { x| x is an odd digit } You say?