### Author Topic: Well-known, but don't look up  (Read 13938 times)

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#### iago

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##### Re: Well-known, but don't look up
« Reply #15 on: March 15, 2008, 05:16:00 pm »
I think the "random" part is important. If you just said, "a lady has two children, one is a son. What are the odds that the other is a son", I think it's more ambiguous. If you went out and found a lady that had a son, then the odds that the other is a son would be, I think, 50%. But if you found a random person, determined that she had one son, and asked what the other might be, that's different.

I think.

#### Nate

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##### Re: Well-known, but don't look up
« Reply #16 on: April 13, 2008, 10:25:18 am »

Order isn't important so there are 3 different states, BB, GG, BG
Each has the same probability P, the sum of the probabilities has to equal 1,
so 3P = 1 or P = .33.

#### Rule

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##### Re: Well-known, but don't look up
« Reply #17 on: July 16, 2008, 03:10:51 pm »
I think the "random" part is important. If you just said, "a lady has two children, one is a son. What are the odds that the other is a son", I think it's more ambiguous. If you went out and found a lady that had a son, then the odds that the other is a son would be, I think, 50%. But if you found a random person, determined that she had one son, and asked what the other might be, that's different.

I think.

No.  If you only sought out a lady who had a son and one other child, and you know nothing else about the lady, then there is no difference.

However, if a lady has one son, and she is pregnant, the probability that the child-to-be is a boy is 50%. It seems, superficially, that the situations are identical.  After all, the lady will eventually have one boy, and one other child.  But giving birth shouldn't change the probability that the other child is a boy.

I'll pose this as a new problem .  Explain the difference that accounts for the difference in probability.
« Last Edit: July 16, 2008, 03:12:47 pm by Rule »

#### Rule

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##### Re: Well-known, but don't look up
« Reply #18 on: July 16, 2008, 03:18:11 pm »

Order isn't important so there are 3 different states, BB, GG, BG
Each has the same probability P, the sum of the probabilities has to equal 1,
so 3P = 1 or P = .33.

? She has one boy.  GG is not a possible state.  You also have to justify why the three actual possible states have equal probability.

#### Rule

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##### Re: Well-known, but don't look up
« Reply #19 on: July 17, 2008, 10:35:05 pm »
Explain the difference that accounts for the difference in probability.

Somehow I think there will be no takers.  lol

#### rabbit

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##### Re: Well-known, but don't look up
« Reply #20 on: July 17, 2008, 10:38:16 pm »
You guys seem to be forgetting that there's also the possibility of hermaphrodites, identical twins, and fraternal twins.