▲ | js2 4 days ago | |||||||
So it's "what is the probability both are girls?" vs. "what is the probability the other is a girl?" and most people will hear the latter and answer 1/2 whereas the question is the former and its answer is 1/3. Do I have that right? | ||||||||
▲ | AnotherGoodName 4 days ago | parent | next [-] | |||||||
"The question writer took all sets of two child families and ruled out the bb case. Then they asked the exact question above" This is 1/3 chance - select gg from [gg,bg,gb]' vs "The question writer came across a girl from a two child family, then they asked the exact question above". This is 1/2 chance - select gg from [gg, gg, bg, gb] with gg listed twice since there's two ways to select a girl from that set; ie. coming across a girl is twice as likely to occur from the gg case than it is either gb or bg. I think that's the clearest wording to get the message across. Either way it's the exact same question but it reasonably has a completely different answer. There's no way to resolve this ambiguity with the question as written. | ||||||||
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▲ | LudwigNagasena 4 days ago | parent | prev | next [-] | |||||||
Those questions are equivalent. What is important is the conditional “… given that I looked at a random child and it was a girl” / “… given that I looked at both children and at least one of them was a girl”. | ||||||||
▲ | SkiFire13 4 days ago | parent | prev [-] | |||||||
The issue with asking whether the other is a girl is how you choose the first one. If you look at one random child, see it's a boy and exclude the family, even though the other child may be a girl, then you get the 1/2 probability. If however in that case you also look at the second child, see that's a girl and consider the family anyway, then you get the 1/3 |