A man visits a couple who have 2 children. one of the children, a boy, comes into the room. find the probability <math>p</math> that the other is also a boy.

(a)1/3

(b)2/3

(c)1/2

(d)3/4

Solution by Arjun Suresh

Since, it's given that the first one is a boy, the second event is independent of the first and the probability is 1/2. Had it been "one of the children is a boy" instead of "first one is a boy" then the probability of two children being boys would have been 1/3 (sample space BB, BG, GB).




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A man visits a couple who have 2 children. one of the children, a boy, comes into the room. find the probability <math>p</math> that the other is also a boy.

(a)1/3

(b)2/3

(c)1/2

(d)3/4

Solution by Arjun Suresh[edit]

Since, it's given that the first one is a boy, the second event is independent of the first and the probability is 1/2. Had it been "one of the children is a boy" instead of "first one is a boy" then the probability of two children being boys would have been 1/3 (sample space BB, BG, GB).




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