Permutations and Combinations Basics

Before we are going to solve the problems on Permutations and Combinations lets understand the basics.


Permutations: The different arrangements of a given number of things by taking some or all at a time, are called permutations.
Ex: Take a, b , c are 3 letters and arrange the 2 letter words  with these letters.


Ans:                ab , ac , ba , bc , ca , cb


How to find number of Permutations ?
Ans:  Number of all permutations of n things , taken r at a time, is given by :
      



                                    

  Here n! = n (n-1)(n-2).................................1.

            3!= 3*2*1 = 6

Ex:          

Ans :                                

Combinations: Each of the different selections which can be formed by taking some or all of a number of objects, is called a combination.
Ex: Take a , b, c are three persons . we want to select 2 out 3 . then the possible selections are ab , bc , ca.
Note: Here ab and ba both are same.
How to find number of Combinations ?



Ex:                        

Ans:

******* we are going to add more examples very soon********************

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