# Permutation Combination Formulas Concepts & Problems pdf IBPS CHSL:-

In this Permutation Combination Formulas Concepts & Problems, we will learn some basic counting techniques which will enable us to
answer the questions without actually listing the objects or the things arrangement.
In fact, these techniques will be useful in determining the number of different ways of
arranging and selecting the objects without actually listing them. First of all, we study some fundamental principles and notations. Fundamental Principles of Counting
(a) Addition principle—If an event can occur in m different ways and a second event in n
different ways, then either of the two events can occur in (m + n) ways provided only one event can occur at a time.
(b) Multiplication principle—If an event can occur in m different ways and if corresponding to each way of occurring of this event, there are n different ways of the second event, then both the events can occur simultaneously in (m × n) different ways.Permutation Combination Formulas Concepts & Problems.

 Permutation
 A permutation is an arrangement in a definite order of a number of objects taken some or all at a time. The number of permutations of n different objects taken r at a time, where 0 < r ≤ n and the objects do not repeat is n(n – 1) (n – 2) … (n – r+ 1), which is denoted by p(n, r) or n pr,
 Combination
 A selection which can be formed by taking some or all of number of objects at a time irrespective of the order of their arrangements, is called a combination. Theorem—The number of all combinations of n distinct objects taken r at a time, is denoted n! by symbol nC r == C(n – r). (n – r) ! r ! Since, each combination consists of r different things, which can be arranged among themselves in r ways.

Permutation & Combination Formulas Concepts pdf