Instant K4rma:

Kuchinawa212:
Well, one could be a goat if you want to find a loophole.

I agree. The second child is a goat, isnt it? Damnit, I should have know.

*laughs* I suppose now we have to assume the gender of the goat

It depends. Do we include the first kid in the equation?

If so, 33%.

If not, 50%.

Easy.

Jerious1154:
Think of the problem this way:
Instead of thinking "one is a boy" think "they are not both girls". Both mean the same thing.
If they are not both girls, then obviously there is a 33% chance that they are both boys.

The reason most people think that its 50% is because they interpret "one is a boy" as "the first one is a boy". That's not what it means. It means that at least one is a boy, but its still equally likely that it could be either, and half as likely that it could be both.

Oooooh, didn't think of that.

Real answer is 50%

However, based on the wording of the thread it would be 0% "A women has two kids, one is a boy, what are the odds the other is also a boy?" if its a word problem its 0 if its a real question than 50%

Kuchinawa212:
Well, one could be a goat if you want to find a loophole.

Well, I said one could be a flipper armed freak of nature. Goat is also possible.

It has nothing to do with the gender of either child individually. The only deciding factor is whether the sperm that fertilizes the egg has a "X" chromosome or a "Y" chromosome. The chances for both are 50%.

So the answer to the question, regardless of any circumstances of other children, is 50%.

I laughed when i saw this thread, until i realized that you people are serious. For gods sack go outside & do something productive, like playing in traffic.

-M

It's 100%, obviously. It's too bad only 1 other person was smart enough to see that. Boys always win =D

Debatra:

heyheysg:
It's variable probablity, but I'm not sure the question is phrased right,

The oldest kid is a boy?

anyway

Boy Boy is in
Boy Girl is in
Girl Girl is out
Girl Boy is in

So it's 33%

And the difference between "Boy Girl" and "Girl Boy" is...

Assuming this is a statistical question without empirical basis
or not a biological question

You still have to account for the fact that the children will be of different ages
Even twins aren't born at the exact same time

I know it's counter-intuitive, but the answer is 33%, I believe, for reasons that have been stated.

I actually found the famous '3 doors' riddle easier to comprehend (it was in that crappy film 21: 3 doors, fabulous prize behind one, crap behind the others, you pick a door, you're shown what's behind one of the other doors, then asked if you want to change your choice; intuitively you'd think it wouldn't matter, but you should always change). Made my brain hurt figuring out why, but I got there!

Hold on, after puzzling about this for a while, i thought of an alternative...

1/2 chance of first child being girl ---> 100% chance of boy

chance of the GB 50%

1/2 chance of boy ---> 1/2 chance of girl ---> 25% chance of BG

1/2 chance of boy ---> 1/2 chance of boy ---> 25% chance of BB

25%?

I'm going to have to go with 50% on this one. No other answer seems logical.

MGlBlaze:

Naheal:
I pray that this isn't an honest question.

As do I.

I think it's because so many people label independent events as dependant events and believe that probability as a 'intelligent conscious memory' to it that means one thing has a greater chance of happening if another thing has already happened a bunch of times, like flipping a coin and landing heads 5 times. The chance of getting another heads is still 50% for God's sake.

Yeah its funny how people take ideas from quantum mechanics and think they apply to the macro world of causality in similar fashion.

waggmd:

Azraellod:
The options at the start can be organised like this.

B - B 25%
B - G 25%
G - B 25%
G - G 25%

At least one of them is a boy.

B - B 33%
B - G 33%
G - B 33%
G - G 0%

Thus, the probability of the other sibling being a boy is 33%

And thus this is correct.

Edit http://en.wikipedia.org/wiki/Boy_or_Girl_paradox skip down to the scientific investigation section.

* Mr. Jones has two children. The older child is a girl. What is the probability that both children are girls?"
* Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?

Two versions of the question from that wikipedia section.

Notice how both are different than the question asked.

The probability in the wikipedia article refers to a question involving BOTH kids. The question asked by the creator of this topic was directly related to ONE child.

Child a is boy.

Child b is boy (50%)
Child b is girl (50%)

The question in this case doesn't link both kids. Word the question differently and it would but until the question is reworded then the 33% is false. In this case it is worded like question one in which case as wikipedia confirms, it is in fact 50%.

Among most mammals, the birth count of males is the highest.

So i am going whit 50%, since there is no higher reasonable option.

If you think that it's 33%, then you are wrong.

See, if you accept that there are three outcomes:

Boy/Girl
Girl/Boy
Boy/Boy, then you -are- including the previous event. HOWEVER, there is one problem:

Girl/Boy has a 0% chance of occuring. Because the first child in question is defined as a boy.

So you have three outcomes, of which one has 0% chance of occuring.

The point is, logically excluding an outcome does not alter the chance of that outcome occuring. Just because you can say girl/girl did not happen doesn't change it's probability -of- happening.

Your inability to sort which is which does not affect this.

(altho technically it isn't 50/50 as the chance of a male birth vs female birth is slightly changed)

DracoSuave:
If you think that it's 33%, then you are wrong.

See, if you accept that there are three outcomes:

Boy/Girl
Girl/Boy
Boy/Boy, then you -are- including the previous event. HOWEVER, there is one problem:

Girl/Boy has a 0% chance of occuring. Because the first child in question is defined as a boy.

So you have three outcomes, of which one has 0% chance of occuring.

The point is, logically excluding an outcome does not alter the chance of that outcome occuring. Just because you can say girl/girl did not happen doesn't change it's probability -of- happening.

Your inability to sort which is which does not affect this.

No... the order in which the boy came wasn't defined. It simply states that one of the children is a boy. Since the thing lacks a 0 option, one should assume that the question means that at least one is a boy, meaning the g/b is a viable option.

Male to female birth ration used to be 1050/1000 but males have higher mortality rate so as you look at older populations, the proportion of men to women shifts to favor women.

0%, first off it starts of stating she HAS (present tense meaning they are already born) two kids, and ONE is a boy. Therefore the other must be a girl.

OT: In all seriousness, heyheysg is right (he is post number 11 jsut for reference)

Gmano:

DracoSuave:
If you think that it's 33%, then you are wrong.

See, if you accept that there are three outcomes:

Boy/Girl
Girl/Boy
Boy/Boy, then you -are- including the previous event. HOWEVER, there is one problem:

Girl/Boy has a 0% chance of occuring. Because the first child in question is defined as a boy.

So you have three outcomes, of which one has 0% chance of occuring.

The point is, logically excluding an outcome does not alter the chance of that outcome occuring. Just because you can say girl/girl did not happen doesn't change it's probability -of- happening.

Your inability to sort which is which does not affect this.

No... the order in which the boy came wasn't defined. It simply states that one of the children is a boy. Since the thing lacks a 0 option, one should assume that the question means that at least one is a boy, meaning the g/b is a viable option.

The order in which the boy came wasn't a part of my argument.

You have: One child, and the other child. The one child, you know because you were told. The other child is the unknown one. The order the children came out is irrelevant. They could have come out at the same time. It does not matter.

Just over 50%.

(I read in an article the other day that there are on average 106 men born for every 100 women)

D4zZ:

Glefistus:

Krythe:
50% since it's the male gamete that determines gender.

A second boy, however, does have a 1-2% higher probability of being homosexual. (I WISH I was making that up.)

Later children may not have the potential to grow as large as earlier offspring, and may also suffer intellectually.

You saying homosexuals are small idiots?

not homosexuals, next-in-line children and I think it was scientifically proven that out of some percentage over 50% the first born is generally the smartest of the siblings. I know its not 100% because my friends older brother has stupid written all over his face (and he's not mentally challenged either)

Man decides the baby's gender so the woman doesn't really have a choice, but it would be 50% since sex genes are random and not inherited in the same way as say, hair colour.

Well, it doesn't matter if more men are born than women because statistically men die younger anyway.

I just realized somebody already mentioned this

49.8% looking at the worlds gender ratio

Manicotti:
The birth of each is an independent event. For simplicity's sake, it's the same as flipping a coin, and we're being asked the chance that we're getting two of a kind. 50% per result for each of 2 results = .5 * .5 = 25% chance that the results will be the same.

So there is a 75% chance that the other child is a girl? That really doesn't add up. It is a 50-50 chance of boy or a girl. It is regardless of how many children she has.

A trick question our biology teacher used in an exam, funnily enough.
50%, of course, since the first kid is already defined as a boy.
He doesn't matter for the second kid's gender.

Now, if you were to ask "what are the odds both children are boys?" without defining the first one as a boy, then it'd be 25%.

shewolf51:
50% since the chances of getting a boy or girl in general is based on whether the egg receives either the X or the Y chromosome.

So unless the second child is a fraternal twin, then that is my answer.

You've got it backwards. The egg is always an X chromosome. The sperm is what determines, since it can be either X or Y

Fairly sure that the wikipedia article linked too explained that both the 50% answer and the 33% answer are valid, depending on how you view the question.

Wouldn't we also need to know who the father is and what his semen quality is like?

Seldon2639:

shewolf51:
50% since the chances of getting a boy or girl in general is based on whether the egg receives either the X or the Y chromosome.

So unless the second child is a fraternal twin, then that is my answer.

You've got it backwards. The egg is always an X chromosome. The sperm is what determines, since it can be either X or Y

Actually no, he said it depends on the semen.

We should all agree that the question is badly worded, as apparently there are many different interpretations of it.

That said, I think 50% as we don't care anything about the one we know about and you're over complicating it taking into account different birth-rates, twins etc. without the question mentioning them.

The fact that one kid is a boy has no influence on the gender of the other kid. But yeah, the question is badly worded, and therefore could have several correct answers depending on the interpretation.

0.5, 50%, 1/2...