Permutations

P(n,r) = \frac{n!}{(n-r)!}

Description

Number of ways to arrange r items from n items where order matters.

Variables

Symbol	Meaning
`n`	Total number of items
`r`	Number of items to arrange
`!`	Factorial

Example

Problem

Arrange 3 from 5 items

Solution

P(5,3) = 5!/(2!) = 60

Real-World Applications

Probability
Combinatorics
Cryptography