Combinations and permutations are foundational concepts in probability and statistics, describing the number of ways to select or arrange items from a set. This combinations and permutations calculator computes C(n,r), the number of ways to choose r items from n when order doesn't matter, and P(n,r), the number of ways to arrange r items from n when order does matter. It also displays the factorial values used in these calculations, helping you understand the underlying math. Students studying probability, statisticians designing experiments, or anyone solving problems involving lottery odds, card games, or arrangement possibilities will find instant, accurate results here.