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How do I find the probability of a three children family having exactly two boys given that at least one of their children is a boy?

Do I use the dependent formula $$P(A \text{ and } B) = P(A) \times P(B \text{ given that }A \text{ has occurred})$$ or do I use the conditional probability form of $P(B|A)$?

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    The first works just fine.2012-05-17
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    *Given that* indicates conditional probability.2012-05-17
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    If you haven't internalized the concepts it will be easier to build intuition if you enumerate the sample space and count the desired outcomes. E.g. at least one boy excludes GGG from the unrestricted set of eight {BBB, BBG, ... }.2012-05-17

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