Permutation & Combination Class XI Chapter 7 Explanation of Formulas and basic points related to the permutation and combination class XI chapter 7, method of arrangement and selection of the objects. Fundamental Principal of Counting : If an event can occur in m different ways, following which another event can occur in n different ways, then the total number of occurrence of the events in the given order is m x n. This principal can be generalized for any finite number of terms. If an event can occur in m different ways, following which another event can occur in n different ways, following which another event can occur in p different ways, and so on. Then the total number of occurrence of the events in the given order is m x n x p………….. For Example: A person have 3 pants and 2 shirts. How many different pairs of a pant and a shirt, can he dress up with? Sol. There are 3 ways to select the pant. He can either select pant P 1 , P 2 or P 3 . Si