כיצד לחשב את Combinations Permutations

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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.

מדריך שלב אחר שלב

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