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Question
A couple has two children, Find the probability that both children are females, if it is known that the elder child is a female.
Solution
Let A = both children are girls = [GG]
B = The elder child is a girl = {GG, GB}
P(A ∩ B) = `1/4` and P(B) = `1/2 = 2/4`
∴ `P(A/B) = (P(A ∩ B))/(P(B))`
= `1/4 ÷ 2/4`
= `1/2`
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