# Importance of Permutation and Combination in JEE

Rohan Mathew

Updated on:

Permutation and combination is an important topic for the JEE Main exam. Students can expect 1-2 questions from this topic for the JEE Main exam. So students are advised to have a thorough understanding of the topic. They are recommended to have a proper preparation plan so that they can easily crack this exam. Practising mock tests and previous year question papers is one of the best ways to score high marks for this exam.

When the order does not matter, we say it is a combination. It is a permutation, when the order matters. Selecting items from a group of items, where the order of selection does not matter is called combination. Sometimes students get confused with permutations and combinations. Permutation deals with arranging items in a specific order. Both these terms are related to finding the number of different ways of arranging and selecting objects out of a given number of items, without actually listing them.

General Formula for Combination

Combination is the number of ways an object can be selected from a group. We do not consider the order here. Items can be repeated. The general formula for combination is given by

nCr = n!/r!(n – r)!

Here n denotes the number of objects and r denotes the number of objects taken at that time.

General Formula for Permutation

Permutation is the arrangement of objects in a specific sequence or order and the order of arrangement matters. The general formula is given by

nPr = n!/(n-r)!

nPn = n!

Important Formulas

• nCn = 1
• nC0 = 1
• nCn-r = nCr
•  nCr +  nCr-1 =  n+1Cr

Let us have a look at an example.

Example: Find the number of ways can you allot 5 rooms to 3 men?

In this question, we can see the total 5 rooms are there. First man can select 1 among the 5 rooms available. Similarly the 2nd one will be left with 4 choices and the 3rd one will be having 3 choices.

Number of ways of allotting = 5 × 4 × 3 = 60 ways