Combination and Permutation Calculator

Count ways to select items from a set.

Permutations (Order Matters)

P(n,r) = n!/(n-r)!. Arranging 3 of 5: P(5,3) = 60.

Combinations (No Order)

C(n,r) = n!/(r!(n-r)!). Choosing 3 of 5: C(5,3) = 10.

When to Use

• Permutation: Passwords, rankings
• Combination: Lottery, teams

Key Insight

C(n,r) = P(n,r)/r!.