# N Choose R Combination Notation

The number of possible ways to choose r combinations from n total items is denoted using two parentheses with the variables n and r. A subscript p or c is used to denote whether it is a combination or permutation. A combination indicates that order does not matter, where for a permutation order does matter.

## Formula

The combination formula describes the possible combinations of r elements out of a group of n elements where order does not matter.

## Examples

### Four Choose Two

To calculate four choose two where order does not matter, you can use the formula for combinations. For example if we want to calculate the possible combinations of choosing twp items from the set {♥︎,♦︎,♣︎,♠︎} we can set up the formula:

First we substitute four in for the variable , representing the size of the set. Then we substitute two for the variable , representing the number of items we are choosing.

To double check our work, we can display the six possible permutations of these two items chosen from the set. Note, if order does matter, you can use the formula for permuations.

- { ♥︎, ♠︎ }
- { ♦︎, ♠︎ }
- { ♥︎, ♦︎ }
- { ♣︎, ♠︎ }
- { ♥︎, ♣︎ }
- { ♣︎, ♦︎ }