Rule of product

The elements of the set {A, B} can combine with the elements of the set {1, 2, 3} in six different ways.

In combinatorics, the rule of product or multiplication principle is a basic counting principle (a.k.a. the fundamental principle of counting). Stated simply, it is the intuitive idea that if there are a ways of doing something and b ways of doing another thing, then there are a · b ways of performing both actions.^[1]^[2]

^ Johnston, William, and Alex McAllister. A transition to advanced mathematics. Oxford Univ. Press, 2009. Section 5.1
^ "College Algebra Tutorial 55: Fundamental Counting Principle". Retrieved December 20, 2014.

[transition-1] Johnston, William, and Alex McAllister. A transition to advanced mathematics. Oxford Univ. Press, 2009. Section 5.1

[2] "College Algebra Tutorial 55: Fundamental Counting Principle". Retrieved December 20, 2014.

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