Old 2nd April 2003, 23:27   #361
xzxzzx
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This is getting very interesting. However, your logic is flawed. GB/BG is not the same - well it is, but it's more likely than GG. Ok, let's look at how GG GB BG BB is constructed:

Samples = B/G+B/G
We have two possibilities, and two slots, so we have 4 possibilities (2^2):
code:
B + B/G
G + B/G
then
B + B
B + G
G + B
G + G


If you had three children (2^3):
code:
B/G + B/G + B/G
-
B + B/G + B/G
G + B/G + B/G
-
B + B + B/G
B + G + B/G
G + B + B/G
G + G + B/G
-
B + B + B
B + B + G
B + G + B
B + G + G
G + B + B
G + B + G
G + G + B
G + G + G


Or how about 21 children (assuming 20 of them are girls)
code:
GGGGGGGGGGGGGGGGGGGGG
BGGGGGGGGGGGGGGGGGGGG
GBGGGGGGGGGGGGGGGGGGG
GGBGGGGGGGGGGGGGGGGGG
GGGBGGGGGGGGGGGGGGGGG
GGGGBGGGGGGGGGGGGGGGG
GGGGGBGGGGGGGGGGGGGGG
GGGGGGBGGGGGGGGGGGGGG
GGGGGGGBGGGGGGGGGGGGG
GGGGGGGGBGGGGGGGGGGGG
GGGGGGGGGBGGGGGGGGGGG
GGGGGGGGGGBGGGGGGGGGG
GGGGGGGGGGGBGGGGGGGGG
GGGGGGGGGGGGBGGGGGGGG
GGGGGGGGGGGGGBGGGGGGG
GGGGGGGGGGGGGGBGGGGGG
GGGGGGGGGGGGGGGBGGGGG
GGGGGGGGGGGGGGGGBGGGG
GGGGGGGGGGGGGGGGGBGGG
GGGGGGGGGGGGGGGGGGBGG
GGGGGGGGGGGGGGGGGGGBG
GGGGGGGGGGGGGGGGGGGGB



Quote:
We KNOW for a 100% FACT that the first child is a girl.
Actually, we have no idea (well, there's a two in three chance) if the first child is a girl. We know that ONE of the children is a girl. If we knew the OLDER, or the YOUNGER one is a girl, then we know the other child has a 50% chance.

On another note, Ockham’s razor only really applies to competing theories when they come up with the same answer, or you cannot determine which answer is closer to truth: "Pluralitas non est ponenda sine neccesitate", indeed - note the last word.

Suppose that you have two competing theories which describe the same system, if these theories have different predictions than it is a relatively simple matter to find which one is better: one does experiments with the required sensitivity and determines which one gives the most accurate predictions.

Following that, here is an experiment. I assume that a coin probably has close enough to 50/50 landings to do this:

Flip two coins (or one coin twice), 20 times (or more, if you want to get more accurate), and record the results. Going through the pairs of flips, one at a time, have a friend ask you "is one of the pair of flips heads?" - if it is, mark down what the other flip is. So if the flips are HT (in whatever order), mark one for tails, and if it's HH, mark one for heads.

You will find, on average, that about you will have about 10 markings for Tails, and 5 for Heads, leaving the remaining 5 (which are not marked anywhere, as the answer was "no") with TT. Of course, your results will probably not be exactly this, but it will be close.

Rather than pointlessly argue, TRY IT, and see what you find, unless you think there's something wrong with the experiment.

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Old 3rd April 2003, 00:25   #362
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IT IS FIFTY FUCKING FIFTY.

My GOD cant you see that?

You're making damn CHARTS to show weather it will be a boy or a girl. IT WILL BE ONE OF THEM, WITH EQUAL CHANCES OF IT BEING A BOY.

I dont CARE what a fucking COIN TOSS will show, you have a GIRL already there, YOU CANNOT CHANGE THAT, THUS YOU ARENT "TOSSING" TWO COINS, YOU ARE TOSSING ONE, BECAUSE THE GIRL ISNT GOING TO MAGICALLY CHANGE.

50/50

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Old 3rd April 2003, 02:04   #363
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Quote:
Originally posted by xzxzzx
I don't understand how you can "stand by" two opposing answers, though.

I can stand by them both because I can see both sides of the argument

When you look at it mathematically, you answer is correct, i see that, but when you look at it from a biologist's stand-point, it is 50/50, no questions asked, so depending on the point of view, both answers can be considered correct
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Old 3rd April 2003, 03:14   #364
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The 67% answer is correct, both in actual practice, and mathematically. There are not two answers, there is one. The coin toss experiment is exactly what you would find in real life (assuming children were exactly 50/50, which they are not, but close enough). The point of view is irrelevant. If I had asked the question differently, the point of view would matter. However, it does not. It is not a biology problem.

How can I convince you that it is 67%? Do I need to find some of the countless sites that agree with me?

MY GOD, I EVEN POSTED AN EXPERIMENT FOR YOU. How the FUCK is it not the same as the riddle? Tell me that!

What will it take? Maybe you can post an equivalent experiment, and I will do it?

What you are forgetting is that we are not really solving what sex a child will be, but solving what the sex of two children will be. Because we do not know which of the two children is a girl, the 'problem' is not reduced to one child.

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Old 3rd April 2003, 03:21   #365
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Ok, i guess for the particular question that you are asking, the 2/3 answer is correct. Happy?
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Old 3rd April 2003, 03:36   #366
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"Ok, here's one that should inspire some debate, and is more aligned You meet a long-lost HUMAN friend of yours. She brings along one of her two children, who is a girl. What is the chance that the other child is a boy?"

"What you are forgetting is that we are not really solving what sex a child will be, but solving what the sex of two children will be. Because we do not know which of the two children is a girl, the 'problem' is not reduced to one child."

yes you are. by asking "What is the chance that the other child is a boy?" you are asking us what chance it has of being of the male sex.
One is a girl. that leaves a 50% chance the other is a boy.
It does not matter WHICH one is a girl, it just matters that one of them IS a girl. Leaving it that we are trying to find the probibality of what sex the OTHER child is, which is 50/50.

Now, if you would have said:

"A woman has 2 children. What is the chance they will both be male?"

Then i would agree that there would be a 25% chance on all male, 25% chance on all female, and 50% chance on a boy and a girl.

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Old 3rd April 2003, 06:04   #367
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Delete me

Freedom of speech is the basic freedom of humanity. When you've lost that, you've lost everything.
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Old 3rd April 2003, 06:12   #368
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SSJ4_Gogitta, you are answering the wrong riddle. With that form of the riddle, depending on how you look at it, it is 50%, because which child, and the sex you find, is random. It is not, however (we now know the sex beforehand, and are now eliminating the chance of which sex is being picked), with this:
Quote:
You come up to a couple, and find out that they have two children. You ask, "Is one of those children a girl?". They respond, "yes".
What is the likelihood of the other child being a boy?
Quote:
SSJ4_Gogitta Said:... i would agree that there would be a 25% chance on all male, 25% chance on all female, and 50% chance on a boy and a girl.
Ok, then, we eliminate the all male chance - that leaves 67% for m/f, and 33% for f/f. Right?

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Old 30th April 2003, 04:17   #369
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Good point...very good point....?????
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Old 30th April 2003, 06:37   #370
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If you still don't agree, perhaps these sites can convince you:

http://www.greylabyrinth.com/Puzzles/puzzle054.htm

http://mathforum.org/dr.math/faq/faq.boy.girl.html

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Old 30th April 2003, 07:42   #371
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Wow. Good thread, though frustrating to read towards the end.

The answer to the boy/girl question just depends on how you phrase the question. Ignoring biological factors, family planning, hermaphrodites, and such:

You ask a mother with two kids: "Is one of your children a girl?"
She says yes.
P(2nd child is a boy) = almost 1. If both were girls, most people would respond something like "No, both of them are girls." They'll infer that you meant logical XOR rather than logical OR.

You ask a mother with two kids: "Is at least one of your children a girl?"
She says yes.
P(2nd child is a boy) = 2/3. Xzxzzx explained this case over and over again, but never really phrased the setup correctly.

You meet a mother with two kids. One of them is with her, and is a girl.
Or: You meet a mother with two kids. You find out that the older one is a girl.
Or: Most of the other ways of putting the problem which I've forgotten already that were posted in this thread.
P(2nd child is a boy) = 1/2. Rumata clearly understands this, and is correct.

Anyone care to argue with that?


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Anyone care for a poker probability question that'll take way too long to solve correctly? (Warning: I've got the correct answer, but might be too lazy or absent to explain it.)
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Old 30th April 2003, 13:31   #372
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Everyone knows that the third word in the english language ending in -gry is nugry.... :P

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Old 30th April 2003, 16:07   #373
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Quote:
Originally posted by Winsane
You ask a mother with two kids: "Is one of your children a girl?"
She says yes.
P(2nd child is a boy) = almost 1. If both were girls, most people would respond something like "No, both of them are girls." They'll infer that you meant logical XOR rather than logical OR.
Uh, ok, then the chance is even further from 50%, it is 100% - there is no "chance" at all.

Quote:
Originally posted by Winsane You ask a mother with two kids: "Is at least one of your children a girl?"
She says yes.
P(2nd child is a boy) = 2/3. Xzxzzx explained this case over and over again, but never really phrased the setup correctly.
I think everyone clearly understood the question was "at least one". No one argued it was 100%.

Quote:
Originally posted by Winsane You meet a mother with two kids. One of them is with her, and is a girl.
Or: You meet a mother with two kids. You find out that the older one is a girl.
Or: Most of the other ways of putting the problem which I've forgotten already that were posted in this thread.
P(2nd child is a boy) = 1/2. Rumata clearly understands this, and is correct.
Obviously. You have to predetermine the sex that you want to ask about, and must do so from the selection of the two, not just the child that happens to be brought along.

Oh, and as for the poker probability question, bring it on!

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Old 30th April 2003, 21:03   #374
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The answer of course is 67% for a boy - it's called indirect (or dependend) probability. There was a similar riddle by Maria vos Savant (the person with the highest IQ ever measured) some years ago, that uses Bertram's selection paradoxon to get you into the strange world of dependend probability, that sometimes seems to speak against our 'natural' sense of logic ...


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Old 30th April 2003, 21:44   #375
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So post it!

Freedom of speech is the basic freedom of humanity. When you've lost that, you've lost everything.
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Old 30th April 2003, 22:12   #376
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look here


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Old 22nd September 2003, 20:22   #377
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Old 22nd September 2003, 21:39   #378
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Wow, I remember this thread...

And damn it, it's 2/3! Just TRY IT!

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