Supposedly a friend of yours has 2 children and at least one of them is a boy. What is the probability that the other is also a boy?
Answer
P(B)=P(G)=1/2
P(BB)=P(BG)=P(GB)=P(GG)=1/4
Probability that the other one is a boy = P(B)=1/2
Probability that the other is also a boy, given at least one of them is a boy=P(BB)/[P(BB)+P(BG)+P(GB)]
=(1/4)/(3/4) =1/3
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