Permutations and combinations

Math

Definition

Permutations count the number of ways to arrange items where order matters. Combinations count the number of ways to choose items where order does not matter.

Examples

  • Arranging 3 books on a shelf: permutation = 3! = 6 ways
  • Choosing 3 people from 10 for a committee: C(10,3) = 120 ways
  • A 4-digit PIN where digits can't repeat: P(10,4) = 5040
Key Fact

P(n,r) = n!/(n-r)! (order matters); C(n,r) = n!/(r!(n-r)!) (order doesn't matter)

Related Terms

Basic probability Binomial probability Binomial distribution

Study This Concept

Practice permutations and combinations with free review games in these units:

Algebra 2 Unit 10: Probability and Statistics