Assume that each born child is equally likely to be a boy or a girl. If a family has two children, what is the conditional probability that both are girls? Given that
i. the youngest is girl
ii. at least one is a girl.
Let B= boy G= girl
And let us consider, in a sample space, the first child is elder and second child is younger.
Total possible outcome = {BB, BG, GB, GG} = 4
Let A= be the event that both the children are girls = 1
Therefore P(A) =
Case 1.
Let B = event that youngest is girl = {BG, GG} =2
{Since we have considered second is younger in a sample space}
Therefore P(B) =
And (A ∩ B) = both are girls and younger is also girl = (GG) = 1
Therefore , P (A ∩ B) =
We require
=
= (answer)
Case 2.
Let B = event that at least one is girl = {BG,GB GG} =3
{Since we have considered second is younger in a sample space}
Therefore P(B) =
And (A ∩ B) = both are girls and atlas one is girl = (GG) = 1
Therefore , P (A ∩ B) =
We require
=
= (answer)