Exam Preparation Tips

How to deal with Factorial!! Major mark contributions in Exams !!



The number of sequences that can exist with a set of items, derived by multiplying the number of items by the next lowest number until 1 is reached. In mathematics, product of all whole numbers up to the number considered. The special case zero factorial is defined to have value 0!=1, consistent with the combinatorial interpretation of there being exactly one way to arrange zero objects. The notation n factorial (n!) was introduced by Christian Kramp in 1808.


An arrangement is called a Permutation. It is the rearrangement of objects or symbols into distinguishable sequences. When we set things in order, we say we have made an arrangement. When we change the order, we say we have changed the arrangement. So each of the arrangement that can be made by taking some or all of a number of things is known as Permutation. 


A Combination is a selection of some or all of a number of different objects. It is an un-ordered collection of unique sizes.In a permutation the order of occurence of the objects or the arrangement is important but in combination the order of occurence of the objects is not important.  


  • Factorial=n! = 1*2*3*...*n.
  • Permutation = nPr = n! / (n-r)! 
  • Combination = nCr = nPr / r! =n!/(n-r)! r!


n,r are non negative integers and r

r is the size of each permutation.

n is the size of the set from which elements are permuted.

! is the factorial operator.


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