A family has two children. Knowing that one of them is a girl, what is the probability that the other is also a girl?
As usual, please put your answers in spoilers!
As usual, please put your answers in spoilers!
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Probability Problem for Fun (First One in a While!)
- Thread starter Debater Slayer
- Start date
Father Heathen
Veteran Member
How could the sex of one sibling effect the the sex of another sibling?
This an example of gambler's fallacy?
This an example of gambler's fallacy?
Answering this would require me to spoil the whole question, but I can do it if you'd like.
No, this is a perfectly valid question in probability theory. Its answer is also quite counterintuitive for a lot of people.
Jedster
Well-Known Member
1/2 independent events, knowing one child is a girl is a red herring(irrelevant)
Leaving aside things such as intersex children and genetic predispositions towards a certain gender in specific couples' offspring (which seems to be a real thing, but I have little idea how to measure), I would think that the probability ought to be presumed to be 50%.
Heyo
Veteran Member
We have to look at four (equally probable) cases
boy, boy
boy, girl
girl, boy
girl, girl
Knowing that at least one child is a girl, we can exclude one of them.
From the remaining cases only one has a second girl.
The probability of the second child being a girl is thus 1/3.
boy, boy
boy, girl
girl, boy
girl, girl
Knowing that at least one child is a girl, we can exclude one of them.
From the remaining cases only one has a second girl.
The probability of the second child being a girl is thus 1/3.
Okay, anyone else want to take a stab at this before I post the answer? 
49.9999999999%