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06-10-2008, 11:26 AM
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#1
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Recycles dryer sheets
Join Date: Jan 2008
Posts: 323
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Word puzzle
Bob has two children. One of his children is a boy. What are the odds that bob has a daughter?
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06-10-2008, 11:52 AM
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#2
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Thinks s/he gets paid by the post
Join Date: Dec 2007
Posts: 4,764
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2/3
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06-10-2008, 12:02 PM
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#3
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Thinks s/he gets paid by the post
Join Date: Feb 2006
Posts: 3,895
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assuming neither child is hermaphroditic, i still need more information to answer that question. which one is the transexual?
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"off with their heads"~~dr. joseph-ignace guillotin
"life should begin with age and its privileges and accumulations, and end with youth and its capacity to splendidly enjoy such advantages."~~mark twain - letter to edward kimmitt 1901
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06-10-2008, 12:17 PM
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#4
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Recycles dryer sheets
Join Date: Jan 2008
Posts: 323
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 Quote:
Originally Posted by lazygood4nothinbum
assuming neither child is hermaphroditic, i still need more information to answer that question. which one is the transexual?
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Bob, obviously.
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06-10-2008, 12:33 PM
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#5
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Dryer sheet wannabe
Join Date: Feb 2008
Posts: 23
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50/50.
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06-10-2008, 12:42 PM
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#6
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Moderator
Join Date: Oct 2005
Location: Texas
Posts: 15,624
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Nearly 2/3. It would be 2/3 except that the actual chances that any given birth is a girl is not 50%, but about 48.8% (a 100 in 205 chance, since about 105 boys are born for every 100 girls).
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"Hey, for every ten dollars, that's another hour that I have to be in the work place. That's an hour of my life. And my life is a very finite thing. I have only 'x' number of hours left before I'm dead. So how do I want to use these hours of my life? Do I want to use them just spending it on more crap and more stuff, or do I want to start getting a handle on it and using my life more intelligently?" -- Joe Dominguez (1938 - 1997)
RIP to Reemy, my avatar dog (2003 - 9/16/2017)
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06-10-2008, 12:50 PM
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#7
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Dryer sheet aficionado
Join Date: Mar 2008
Posts: 48
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mutually exclusive events so stats on births will prevail
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06-10-2008, 12:55 PM
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#8
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Moderator
Join Date: Oct 2005
Location: Texas
Posts: 15,624
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There are four possible outcomes for Bob, and to make it simple assume births are 50% boys and 50% girls:
* boy and then girl
* boy and then boy
* girl and then boy
* girl and then girl
If we know nothing, each of these have a 25% likelihood. But knowing one is a boy, we can remove the girl/girl possibility and we are left with three options, each with a 1/3 chance of occurring:
* boy and then girl
* boy and then boy
* girl and then boy
So in 2/3 of the scenarios, Bob has a girl.
__________________
"Hey, for every ten dollars, that's another hour that I have to be in the work place. That's an hour of my life. And my life is a very finite thing. I have only 'x' number of hours left before I'm dead. So how do I want to use these hours of my life? Do I want to use them just spending it on more crap and more stuff, or do I want to start getting a handle on it and using my life more intelligently?" -- Joe Dominguez (1938 - 1997)
RIP to Reemy, my avatar dog (2003 - 9/16/2017)
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06-10-2008, 01:22 PM
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#9
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Dryer sheet aficionado
Join Date: Mar 2008
Posts: 48
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nice, didn't catch on to the elimination requisite
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06-10-2008, 01:32 PM
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#10
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Dryer sheet wannabe
Join Date: Feb 2008
Posts: 23
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Quote:
Originally Posted by ziggy29
If we know nothing, each of these have a 25% likelihood. But knowing one is a boy, we can remove the girl/girl possibility and we are left with three options, each with a 1/3 chance of occurring:
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Say you pick a parent of two, Sue, at random. You ask for the sex of one of her children. According to your answer, there is a 2/3 chance that the sex of the second child is the opposite of whatever Sue answers. If she says she has a girl, odds are her other child is a boy. If she says she has a boy, odds are her other child is a girl.
But if Sue has two boys, she will always say she has a boy. If she has two girls, she'll always say she has a girl. And if she has one of each, she'll pick one at random and say that. In all of those cases, the odds are equal--one in two--that her two children are the same sex.
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06-10-2008, 02:15 PM
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#11
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Moderator Emeritus
Join Date: Jun 2007
Location: At The Cafe
Posts: 6,866
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The odds that bob has a daughter are 0% (zero percent/nada/zilch/no way Jose).
What assumptions have I made?
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06-10-2008, 02:38 PM
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#12
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Thinks s/he gets paid by the post
Join Date: Oct 2003
Posts: 1,200
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The children are not his.
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We are, as I have said, one equation short. – Keynes
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06-10-2008, 02:41 PM
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#13
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Recycles dryer sheets
Join Date: Jan 2008
Posts: 323
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Quote:
Originally Posted by CuppaJoe
The odds that bob has a daughter are 0% (zero percent/nada/zilch/no way Jose).
What assumptions have I made?
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I don't know about your assumptions. Perhaps one of the following:
His wife "had" the kids.
Nobody owns a kid.
You know bob personally.
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06-10-2008, 02:49 PM
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#14
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Give me a museum and I'll fill it. (Picasso)
Give me a forum ...
Join Date: Dec 2006
Location: Dallas 'burb
Posts: 9,059
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I'm glad I don't have kids.  Bob can have as many as he wants.
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There's no need to complicate, our time is short..
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06-10-2008, 11:43 PM
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#15
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Moderator Emeritus
Join Date: Jun 2007
Location: At The Cafe
Posts: 6,866
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Quote:
Originally Posted by Abreutime
I don't know about your assumptions. Perhaps one of the following:
His wife "had" the kids.
Nobody owns a kid.
You know bob personally.
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You and Ronin are thinking out of the box, cool.  I didn't think of those 4 assumptions. I was being literal.
No, I don't know him personally. I assume you made him up. In case the 0% solution is 100% wrong, throw me a bone: This family of four is hypothetical, right?
Sorry, that was off point.
Has anyone else inhaled the coffee dust and crashed to zero?
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06-11-2008, 08:44 AM
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#16
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Thinks s/he gets paid by the post
Join Date: Oct 2003
Posts: 1,200
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I was thinking kidnapper pedophile, but didn't want to stress you parents out.
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We are, as I have said, one equation short. – Keynes
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06-11-2008, 08:58 AM
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#17
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Moderator Emeritus
Join Date: Jun 2007
Location: At The Cafe
Posts: 6,866
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Quote:
Originally Posted by Abreutime
Bob has two children. One of his children is a boy. What are the odds that bob has a daughter?
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First assumption: Abreutime has made no typos in the original post, therefore there are two "Bobs," uppercase Bob and lowercase bob. Next assumption: bob is Bob's son. bbbam1 is so right and a riot in saying "Bob can have as many as he wants." I also agree with P.K. Sublime, "the stats on births will prevail." Assuming bob is "a boy," he has not yet hit puberty and therefore has no children.
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06-11-2008, 09:03 AM
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#18
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Moderator Emeritus
Join Date: Jun 2007
Location: At The Cafe
Posts: 6,866
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Quote:
Originally Posted by ronin
I was thinking kidnapper pedophile, but didn't want to stress you parents out.
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Our last two posts crossed on the net, thanks, I was still coping with hermaphrodites and trannies. This is just like retirement planning, now I need to re-think the assumptions which intersect and crash into the unknown. 
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