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not what it seems
05-12-2008, 09:22 AM
Post: #1
not what it seems

mrs wilkins has two children

call them child a and child b

you are told one of them is a girl

what are the chances that the other one is a girl?

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05-12-2008, 12:22 PM
Post: #2
not what it seems
yur recking me hed

bam bam
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05-12-2008, 12:38 PM
Post: #3
not what it seems
Isn't it just 50/50?

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05-12-2008, 12:40 PM
Post: #4
not what it seems
isn't everything?

bam bam
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05-12-2008, 02:09 PM
Post: #5
not what it seems
survivorfan Wrote:call them child a and child b

Not very imaginative are they?

I have no idea with this one.

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05-12-2008, 03:37 PM
Post: #6
not what it seems
it's not 50/50

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07-12-2008, 10:13 AM
Post: #7
not what it seems
it's 1 in 3

the possibilities are

a = boy b = boy
a = boy b = girl
a = girl b = girl
a = girl b = boy

and the first option is out

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07-12-2008, 02:27 PM
Post: #8
not what it seems
But aren't the second and fourth exactly the same?

Because it wasn't designated in the original question that child a is the girl, or whether it is child b.

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07-12-2008, 03:45 PM
Post: #9
not what it seems
I think if the original question said child a was a girl then it would be 50/50 that child b was also a girl

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07-12-2008, 04:19 PM
Post: #10
not what it seems
Probability depends on the way you define the sample space. It is easy to obtain different answers if you change the sample space. A well- known example is the probability of drawing a random chord in a circle such that its length is greater than the side of the inscribed equilateral triangle. The probability can be 1/4, 1/3 or 1/2 depending on how you define a 'random' chord. None of these answers is more 'correct' than the others; they are all correct if the randomness is defined in a particular way.

Now going to your problem with the two children. If the sample space is the total ways that you could have two children then BB, BG, GB, GG is correct and if you cancel BB then probability of one boy, one girl is 2/3. However, if you take the sample space as having one child, then B or G are the two possibilities, and the probability of a boy is 1/2. So if you ask the question BEFORE the second birth the probability of a boy is 1/2. If you ask the question AFTER both children are born then the probability is 2/3. In other words, probability is not a fixed property of some event, it is a function RELATIVE to a framework of events.


^^I don't understand any of that :thumbsup:

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