⋅ P(B | A): probability of event B occurring, given that event A has already occurred.
⋅ recall: P(A and B) = P(A) ⋅ P(B | A)
then: P(B | A) = P(A)P(AandB)
Probability Tree Diagram
Bag A contains 2 red balls and 3 green balls. Bag B contains 1 red ball and 4 green balls.
A fair die is rolled: if a 1 or 2 comes up, a ball is randomly selected from Bag A;
if a 3, 4, 5, or 6 comes up, a ball is randomly selected from Bag B.
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