Permutation Formula
P(n, r) = n! / (n − r)!
Example
P(5, 2) — Arranging 2 from 5
P(5,2) = 5! / (5−2)! = 120 / 6 = 20
Real-World Uses
- Number of ways to arrange letters in a word
- Number of possible PIN codes
- Race finishing orders
- Password combinations