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#81
03-17-2005, 05:22 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
[ QUOTE ] yes, ever so slightly more than 50-50 the other kid is a boy, it doesnt make it anywhere near 1/3. [/ QUOTE ] awesome we agree. now consider all the ways she can have two kids. boy boy - no. so that leaves sarah, boy boy, sarah sarah, girl. find out the probability of sarah, girl. I think it's 99/299. what do you think? [/ QUOTE ] i think the answer ends at 50-50(approximately)and if im wrong, you can buy me a beer 
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#82
03-17-2005, 05:23 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
[ QUOTE ] [ QUOTE ] yes, ever so slightly more than 50-50 the other kid is a boy, it doesnt make it anywhere near 1/3. [/ QUOTE ] awesome we agree. now consider all the ways she can have two kids. boy boy - no. so that leaves sarah, boy boy, sarah sarah, girl. find out the probability of sarah, girl. I think it's 99/299. what do you think? [/ QUOTE ] i think the answer ends at 50-50(approximately)and if im wrong, you can buy me a beer [/ QUOTE ] What if you're both wrong?
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#83
03-17-2005, 05:24 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
[ QUOTE ] yes, ever so slightly more than 50-50 the other kid is a boy, it doesnt make it anywhere near 1/3. [/ QUOTE ] awesome we agree. now consider all the ways she can have two kids. boy boy - no. so that leaves sarah, boy boy, sarah sarah, girl. find out the probability of sarah, girl. I think it's 99/299. what do you think? [/ QUOTE ] I might be wrong, but I think you should also include girl, sarah. Because the chance of having a Sarah is so unlikely, having two girls gives you two shots at having a Sarah. Note in my math if you asked for the chance of two girls given that the mom has a girl not named Sarah, it's ~1/3.
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#85
03-17-2005, 05:26 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] yes, ever so slightly more than 50-50 the other kid is a boy, it doesnt make it anywhere near 1/3. [/ QUOTE ] awesome we agree. now consider all the ways she can have two kids. boy boy - no. so that leaves sarah, boy boy, sarah sarah, girl. find out the probability of sarah, girl. I think it's 99/299. what do you think? [/ QUOTE ] i think the answer ends at 50-50(approximately)and if im wrong, you can buy me a beer [/ QUOTE ] What if you're both wrong? [/ QUOTE ] then you buy us both a beer
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#86
03-17-2005, 05:27 PM
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Re: Super Duper Extra Hard Brainteaser
sarah girl and girl sarah can be considered the same.
BB BG GB GG are all equally likely. but, we know that one girl is a sarah. for the boy cases, it's obvious who sarah is. for the sarah and other girl case, it doesnt matter which girl is sarah, we just know that one of them is. I should have specified, but it doesnt change the answer IMO.
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#87
03-17-2005, 05:32 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
sarah girl and girl sarah can be considered the same. BB BG GB GG are all equally likely. but, we know that one girl is a sarah. for the boy cases, it's obvious who sarah is. for the sarah and other girl case, it doesnt matter which girl is sarah, we just know that one of them is. I should have specified, but it doesnt change the answer IMO. [/ QUOTE ] I think it changes when you factor in that a girl named Sarah is very unlikely. This is the way I see it. B B B G1 G1 B G1 G2 Note the last combination has two shots at getting a girl named Sarah. Either G1 or G2 could be Sarah.
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#88
03-17-2005, 05:34 PM
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Re: Super Duper Extra Hard Brainteaser
yeah, that's what I'm saying too. word, we agree, now I just have to say it the right way.
have you ever seen conditional probability? the jist of it is that we KNOW that there is a girl named sarah. now we just have to worry about the other one. the question isn't "what are the odds she has a girl named sarah and another girl", it's "GIVEN that we have a sarah, what are the odds we ALSO have a girl (knowing that we can't have two sarahs)"
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#89
03-17-2005, 05:43 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
yeah, that's what I'm saying too. word, we agree, now I just have to say it the right way. have you ever seen conditional probability? the jist of it is that we KNOW that there is a girl named sarah. now we just have to worry about the other one. the question isn't "what are the odds she has a girl named sarah and another girl", it's "GIVEN that we have a sarah, what are the odds we ALSO have a girl (knowing that we can't have two sarahs)" [/ QUOTE ] Scroll up to my post with the math (the latter one). It has all probabilities in it explicitly shown. I think this riddle is over. Done with this thread until we get an answer from OP.
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#90
03-17-2005, 05:44 PM
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Re: Super Duper Extra Hard Brainteaser
[ QUOTE ]
I think this riddle is over. Done with this thread until we get an answer from OP. [/ QUOTE ] The OP has already said he doesn't know the answer, so I'll just fill in and tell you all it's 1/3. Good day.
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