ABSTRACT
M14.1.1. Rules and Formulas of Combinatorics Below are rules and formulas of combinatorics that are useful in solving problems of probability theory. ◮ Rule of sum and rule of product.
Rule of sum. Suppose there is a collection of objects (of arbitrary nature). If an object α can be chosen from this collection in m different ways and another object β can be chosen in k ways, then one can choose either object α or object β in m + k different ways.
