Statistics › Section N · Counting, Bayesian inference, and multiple regression › Topic N.1
Counting, permutations, and combinations
The counting formula from the binomial chapter was borrowed without proof; this is its home. With replacement, without replacement, order or not - a few systematic rules count outcomes too many to list, and with equally likely outcomes, counting IS probability.
In this topic
- Why count?
- The multiplication principle
- Factorials: counting arrangements
- Permutations: ordered selections
- Combinations: unordered selections
- The key question: does order matter?
- Worked example: lottery odds
- Worked example: probability from counting
- The birthday surprise
- Common mistakes to avoid
- Key takeaways
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