learn.howToCalculate
learn.whatIsHeading
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.
단계별 가이드
- 1Permutations (order matters): P(n,r) = n! / (n−r)!
- 2Combinations (order irrelevant): C(n,r) = n! / (r!(n−r)!)
- 3Rule of thumb: if you can swap two items and get a different result, use permutations
풀어진 예시
입력
Choose 3 from 10 (order matters)
결과
720
P(10,3) = 10×9×8 = 720
입력
Choose 3 from 10 (order irrelevant)
결과
120
C(10,3) = 720/6 = 120
입력
Lotto: 6 from 49
결과
13,983,816
C(49,6)