Permutation

A permutation is a selection of items in which the order matters. The number of ways to arrange r items chosen from n distinct items is nPr = n! ÷ (n − r)!. Permutations are used to count orderings — finishing positions in a race, passwords, or seating arrangements — and are always at least as numerous as the matching combinations.

Example: The number of 3-letter arrangements from A, B, C, D is 4P3 = 4! ÷ 1! = 24.