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# Rule of Sum and Rule of Product

The Rule of Sum (Addition Principle) and Rule of Product (Multiplication Principle) are principles of counting that are used to build up the theory of enumerative combinatorics.

Rule of Sum / Addition principle: If there are $$n$$ ways of doing something, and $$m$$ ways of doing another thing and the two things cannot be done at the same time, then there are $$n+m$$ ways to choose one of these actions.

Rule of Product / Multiplication principle: If there are $$n$$ ways of doing something, and $$m$$ ways of doing another thing after that, then there are $$n\times m$$ ways to perform both of these actions.

Note by Arron Kau
2 years, 11 months ago