## Permutation and Combination

**Permutations and Combinations-**

‘Permutations and Combinations’ is the next post of my series Topics in IB Mathematics.It is very useful and interesting as a topic. It’s also very useful in solving problems of Probability. To understand Permutations and Combinations, we first need to understand Factorial.

**Definition of Factorial- ** If we multiply n consecutive natural numbers together, then the product is called factorial of n. Its shown by n! or by

for example :

**Some Properties of Factorials-
**(i) Factorials can only be calculated for positive integers at this level. We use gamma functions to define non-integer factorial that’s not required at this level

(ii) Factorial of a number can be written as a product of that number with the factorial of its predecessor

(iii) you can watch this video for the explanation.