Permutations and Combination Permutations and Combination is one section of the CAT Quantitative Aptitude which needs the least number of formulae and the maximum amount of logic. This topic is asked in almost every competitive exam, so don’t take the risk of avoiding it. After reading this article you will be familiar with Permutation and Combination. Definition of Permutation : Permutation is defined as the arrangement of r things that can be done out of total n things. Formula of Permutation Permutation is denoted by nPr it is equal to n!/(n-r)! Defination of Combination: Combination is defined as selection of r things that can be done out of total n things. Formula of Combination Combination is denoted nCr it is equal to n!/r!(n-r)! Fundamental principle of counting Product Rule: If an activity A can be done in “m” ways and an another activity “B” can be done in “n” ways, A and B together can be done in “m x n” ways Example: How ma...