# Counting and Probability

### Learn all about Counting and Probability!

## Counting

There are 4 branches in counting which are:

**-Factorial Notation: **We use factorial notation for a simple way of writing the product of all the positive whole numbers up to a given number.

**-Basic Principles of Counting*** (Addition and Multiplication Rules):* We use these basic principles to develop a few counting techniques. Such techniques will enable us to count the following, without having to list all of the items.

**-Permutations: **An arrangement (or ordering) of a set of objects is called a permutation. (We can also arrange just part of the set of objects.) The order that we arrange the objects is important.

**-Combinations (Unoredered Selections): **A combination of *n* objects taken *r* at a time is a selection which does not take into account the arrangement of the objects. That is, the order is not important.

## Probablity

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## Example

**FACTORIAL NOTATION: **n factorial is defined as the product of all the integers from 1 to *n *(the order of multiplying does not matter) .

We write "*n* factorial" with an exclamation mark as follows: n!

*n*! = (*n*)(*n* − 1)(*n* − 2)...(3)(2)(1)

**5! = 5 × 4 × 3 × 2 × 1 = 120**