Explanation

These are methods to count arrangements or selections without listing all possibilities.

Permutation: order matters
Example: Arranging 3 books (A, B, C) → ABC, ACB, BAC, …

Combination: order does not matter
Example: Choosing 2 friends from 3 (A, B, C) → AB, AC, BC

Formulas:

• Permutation: nPr = n! / (n − r)!

• Combination: nCr = n! / [r! (n − r)!]

Where n = total items, r = items chosen, ! = factorial