A woman has two kids. One is a boy. What are the odds the other is a boy?

H/T and T/H are not 2 heads in a row...

I know.

http://en.wikipedia.org/wiki/Gender_imbalance

I know it's pineappleing Wikipedia, but seriously, how the hell can you think twice as many female babies are born as male babies?

Exactly, it IS Wiki. Get another source and I'll actually read it. Something that ends with a .edu would be nice.

Just because you don't want T/T, that doesn't mean it's eliminated from the list of possible outcomes.

Using a RNG...

0 1
1 0
1 0
1 0
1 1
1 1
0 0
0 1
1 0
0 0
1 1
0 0
1 1
1 1
1 0
0 1
1 0
1 1
1 0
0 1
0 0
0 1
1 1
0 0
0 1
1 0
1 0
0 1
1 1
1 1
1 0
0 1
0 1
0 1
1 0
1 0
0 0
1 0
1 0
1 0
0 0
0 1
0 0
1 0
0 0
0 0
0 0
1 0
0 1
1 0

Number of 01/10: 28, or 56%
Number of 00: 11, or 22%
Number of 11: 11, or 22%

As the number of samples increases, the probabilities would approach 50%, 25%, and 25%.

Khoi: Four coins being all heads is .5^4, not .5^5.

Also, sperm is either X or Y with a 50% chance, while an egg is definitely X.

Just because you don't want T/T, that doesn't mean it's eliminated from the list of possible outcomes.

Using a RNG...

0 1
1 0
1 0
1 0
1 1
1 1
0 0
0 1
1 0
0 0
1 1
0 0
1 1
1 1
1 0
0 1
1 0
1 1
1 0
0 1
0 0
0 1
1 1
0 0
0 1
1 0
1 0
0 1
1 1
1 1
1 0
0 1
0 1
0 1
1 0
1 0
0 0
1 0
1 0
1 0
0 0
0 1
0 0
1 0
0 0
0 0
0 0
1 0
0 1
1 0

Number of 01/10: 28, or 56%
Number of 00: 11, or 22%
Number of 11: 11, or 22%

As the number of samples increases, the probabilities would approach 50%, 25%, and 25%.

Khoi: Four coins being all heads is .5^4, not .5^5.

Also, sperm is either X or Y with a 50% chance, while an egg is definitely X.

Ohp, my bad. But yeah, it's ____ * .5^4

I know.

I read your post wrong. (or rather, hit reply 2 seconds too soon.)

My edit:

But if you aren't given that one of them is heads, then you can't rule out T/T

edit: actually in sicnarf's example, it's still 50% because you are given that the first coin is heads, so you rule out T/T and T/H. So we're left with:

H/T
H/H

Still a different question though.

I think I misunderstood the question previously.

Let me try the example I gave on irc.

First I gave the coin example.

And then I said "Okay, a woman has a child. It is a boy!"
Then I said "She's about to have another one. What is the chance that the new child she has is a boy?"

So, answer my question

that's 50%. But that's not the question here

Exactly, it IS Wiki. Get another source and I'll actually read it. Something that ends with a .edu would be nice.

I edited my post. Still amazed that you need a .edu source to believe that there are roughly the same number of male babies as there are female babies o_o

And since people are ninjaing like crazy, please look at this question again.

A woman has two kids. At least one is a boy. What are the odds that they are both boys?

If Opeth had asked this, he would have been correct.

that's 50%. But that's not the question here

Can you clarify the question, I'm not so sure I understand it, then.

:f6:

I edited my post. Still amazed that you need a .edu source to believe that there are roughly the same number of male babies as there are female babies o_o

And since people are ninjaing like crazy, please look at this question again.

A woman has two kids. At least one is a boy. What are the odds that they are both boys?

If Opeth had asked this, he would have been correct.

Of course, I don't trust websites with .com in them.

I edited my post. Still amazed that you need a .edu source to believe that there are roughly the same number of male babies as there are female babies o_o

And since people are ninjaing like crazy, please look at this question again.

A woman has two kids. At least one is a boy. What are the odds that they are both boys?

If Opeth had asked this, he would have been correct.

Well, while the question's still cryptic, there's "nothing" wrong with it.

Can you clarify the question, I'm not so sure I understand it, then.

:f6:

A woman has two kids. One of them, not stating the first nor the last, is a boy. What are the chances that the other child is a boy?

It's 50% because a sperm cell has x/y so it's 50/50
I doesnt matter if one is a boy, the other is unknown..
It's like scrolling in maplestory.. When your done scrolling the first and it succed the other has a chance of failing or passing
/truth

Of course, I don't trust websites with .com in them.

You don't have to trust the website. Holy pomegranate, it's common knowledge that male/female births are roughly 1:1. I used Wikipedia because while it often has specific facts or data wrong, something prominently at the top of the page with absolutely no contest or even a [citation needed] tag is not going to be wrong and sit up there without anyone editting it.

Honestly, use Google and do your own research. I don't even know what to tell you, I'm just flat out ing at your claim.

It's 50% because a sperm cell has x/y so it's 50/50
I doesnt matter if one is a boy, the other is unknown..
It's like scrolling in maplestory.. When your done scrolling the first and it succed the other has a chance of failing or passing
/truth

The thing is, you don't scroll one scroll here.

You scroll two scrolls, both with 50% rate to work, no possibility to break. You know that one of them worked. What are the chances the other worked?

The thing is, you don't scroll one scroll here.

You scroll two scrolls, both with 50% rate to work, no possibility to break. You know that one of them worked. What are the chances the other worked?

Individually, 50%. Grouped together, 33% chance that they both worked.

it is called independent assortment in genetics. each child has a 50% chance of being a boy or a girl independently of the the previous offsprings. the chance is 50% of the second being a boy.

-- l X l Y
X l XX l XY
---------------
X l XX l XY

as you can see each child has a 50% chance of being boy or girl. and the result of baby 1 doesnt affect the chances of baby numero dos.

bio class dismissed

God people look at the original problem.

One of the kids is a boy

so these are your only options:

B/B
B/G <-
G/B <-

The two with the arrows ARE separate since its only specified that one of them is a boy and you aren't told which.

So simple math, out of 3 distinct possibilities only 1 works... what are the odds then? cough1/3cough.

And to those of you who say that its 50%:

Its only 50% if you're told that the first kid is a boy or a girl. But since you dont know which of the kids is which, you have those three separate possibilities not just two possibilities.

doesnt matter, its a genetics questions and each child is independent from the other. be it the first or the second the chances of it being a boy is 50%

This is kinda like if a coin gets head 5 in a row. What is the next flip going to be? Most people would say tails, but the coin doesn't know that. There is an equally chance of getting a heads again. The same here, there a equally likely chance of getting a boy or girl. Actually, the real percentages of guy to girl are 52%ish to 48%ish, respectively.

God people look at the original problem.

One of the kids is a boy

so these are your only options:

B/B
B/G <-
G/B <-

The two with the arrows ARE separate since its only specified that one of them is a boy and you aren't told which.

So simple math, out of 3 distinct possibilities only 1 works... what are the odds then? cough1/3cough.

And to those of you who say that its 50%:

Its only 50% if you're told that the first kid is a boy or a girl. But since you dont know which of the kids is which, you have those three separate possibilities not just two possibilities.

Ah, but the question is not how many possibilities can be there. It's asking for the gender of a separate child from the other. If the order had any importance, yes, 1/3.

However... We have this two separate possibilities:

OUTCOME #1
Child #1 = Boy
Child #2 = Unknown

Child number 2: 50% chance to be boy - 50% chance to be girl

OUTCOME #2
Child #1 = Unknown
Child #2 = Boy

Child number 1: 50% chance to be boy - 50% chance to be girl

I can't see why it's harder to give birth to another male after giving birth to another. Because, after all, probability is about that.