probability and statistics
Combinatorics and counting
How to count without listing — permutations, combinations, inclusion–exclusion.
5 lessons
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Lessons in sequence
Work through these in order—each lesson builds on the previous one.
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Lesson 1 of 5
Counting principles
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Lesson 2 of 5
Permutations and arrangements
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Lesson 3 of 5
Combinations and the binomial coefficient
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Lesson 4 of 5
Inclusion–exclusion principle
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Lesson 5 of 5
Pigeonhole and its surprises