Discrete Math › Section D · Counting › Topic D.4
Combinations and permutations
Choosing a team and choosing a team with ranked positions are different questions with different answers. Permutations count ordered selections, combinations count unordered ones, and one division links the two.
In this topic
- Does order matter?
- Arranging everything: n factorial
- Ordered selections: k-permutations
- Unordered selections: the formula for n choose k
- Worked example: a committee with a chair
- The quotient principle
- Arrangements with repeated letters
- Worked example: hands of cards
- Choosing the right tool
- Common mistakes to avoid
- Key takeaways
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