Statistics · Probability
Chapter 1 · 3
The idea
Set notation for events
Writing events with set notation — intersection ∩, union ∪ and complement ′ — matching each to a region of a Venn diagram, and the probability rules that go with them (P(A′) = 1 − P(A), P(A ∩ B′) = P(A) − P(A ∩ B)).
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Statistics · Probability
Set notation for events
Writing events with set notation — intersection ∩, union ∪ and complement ′ — matching each to a region of a Venn diagram, and the probability rules that go with them (P(A′) = 1 − P(A), P(A ∩ B′) = P(A) − P(A ∩ B)).
Why it works
Events are sets
"What's the probability that happens but doesn't?" — English gets clumsy fast when events start combining, and clumsiness costs marks. The fix is that an event is just a set of outcomes, so the language of sets gives a precise, compact way to describe any combination. Three symbols do almost all the work:- Intersection — outcomes in both and (" and ").
- Union — outcomes in or or both (" or ").
- Complement — outcomes not in ("not ").
Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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