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This is a probability textbook, and this is about conditional probability. I don't understand this example 1.3-4, specifically that I don't understand how they calculate P(A|B). What's the logic behind?

Beacon
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    I looked at your profile. You haven't upvoted or accepted a single answer to any of your nine questions.. – Derek Luna Jan 12 '20 at 06:54

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The probability that $B$ occurs multiplied by the probability that $A$ occurs given that $B$ has occured is the probability that both $A$ and $B$ occur. In the example above, $A \cap B = A$ since the intersection is only the possiblities where the sum is $3$, precisely event $A$.

$P(B) P(A | B) = P(A \cap B) = P(A)$ leads to the textbook equations.

Derek Luna
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