so P(A|B) = P(A intersect B)/ P(B).(adsbygoogle = window.adsbygoogle || []).push({});

so, P(A intersect B) is the same as P(A) * P(B) right? so doesn't the P(B) always cancel out, and the answer will always be P(A)? That doesn't makes sense at all....

for example: A family has 2 children, and all possibilites are equally possible.

boy boy, boy girl, girl girl, girl boy.

what is the probability of getting Both boys, given that at least one is a boy.

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ok, so since each is equally possible, then there is 1/4 chance for each outcome.

and to have at least one boy, there is 2 chances, out of the 4 chances, which makes that 1/2.

so plug in the formula, and I get the wrong answer....(1/4 * 1/2)/1/4....which is wrong...

the book says the answer is 1/3...

so how do they do that? I dont understand the formula.

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# Homework Help: I dont understand how conditional probabilty works

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