Conditional probability and two-way tables

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Learn it "Given that…" (conditional probability) means you only look at that row or column: P(A | B) = (number in A and B) ÷ (number in B). Note P(A | B) is usually not P(B | A).

Example: Grade 8: 20 play a sport, 10 don't. P(sport | Grade 8)?

Only Grade 8 counts: 30 students.
20 of them play a sport.
$\frac{20}{30} = \frac{2}{3}$.

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