Как да изчислим Combinations Permutations

Какво е Combinations Permutations?

Combinations count ways to choose items where order does not matter. Permutations count ways where order does matter. Both use factorials and appear in probability, statistics, and combinatorics.

Ръководство стъпка по стъпка

1. 1Permutations (order matters): P(n,r) = n! / (n−r)!
2. 2Combinations (order irrelevant): C(n,r) = n! / (r!(n−r)!)
3. 3Rule of thumb: if you can swap two items and get a different result, use permutations

Worked Examples