Counting

Overview

Feature	nPr (Permutation)	nCr (Combination)
Meaning	Arrangements of items where order matters	Selection of items where order does not matter
Formula	$P(n, r) = \frac{n!}{(n - r)!}$	$C(n, r) = \frac{n!}{r!(n - r)!}$
Common Use	Creating passwords, seating charts, or race rankings (1st, 2nd, 3rd)	Choosing a committee, drafting a team, or selecting lottery numbers
Relation	$P(n, r) = C(n, r) \times r!$	$C(n, r) = \frac{P(n, r)}{r!}$