The fundamental counting rule
This section is devoted to counting the number of possible ways to select several objects, each from a set of distinct elements. We will first focus on the case of just two sets before extending it to an arbitrary number of sets.
Definition – the Cartesian product
The set of ordered pairs A × B = {(a, b) : a A, b B}, with component a as an element from set A and the second component b from set B, is called the Cartesian product of sets A and B:
This chapter is all about counting the number of elements in sets. Recall from Chapter 1, Key Concepts, Notation, Set Theory, Relations, and Functions that the cardinality of a set is the number of elements in the set. Cartesian products are interesting things to count because we can count the number of ways of choosing one element from set A and another element...