Factorial, Permutation & CombinationEkam and Rahul A.

What is Probability?

Probability is the extent to which something is probable; the likelihood of something happening

Factorial

A factorial is the product of an integer and all the integers below it

An example is, factorial four (4!; 4 x 3 x 2 x 1) is equal to 24.

Permutation

Permutation: a way, especially one of several possible variations, in which a set or number of things can be ordered or arranged

Ex. Consider, four students walking toward their school entrance. How many different ways could they arrange themselves in this side-by-side pattern?

Answer: The number of different arrangements is 24 or 4! = 4 x 3 x 2 x 1. So there are 24 different permutations or arrangements of how the students can walk

1,2,3,4 2,1,3,4 3,2,1,4 4,2,3,1

1,2,4,3 2,1,4,3 3,2,4,1 4,2,1,3

1,3,2,4 2,3,1,4 3,1,2,4 4,3,2,1

1,3,4,2 2,3,4,1 3,1,4,2 4,3,1,2

1,4,2,3 2,4,1,3 3,4,2,1 4,1,2,3

1,4,3,2 2,4,3,1 3,4,1,2 4,1,3,2