A woman has two kids, one of them is a girl

**Janszoon** · 03-04-2013, 10:45 PM

Quote:

Originally Posted by Tuna

more productive than that 'MB was so much better back in the day' delusion youve been under

answer is 33% cause there's four different possibilities:

BG
GB
BB
GG

Because one of them is already a girl, that dismisses the possibility of BB, leaving:

BG
GB
GG

Since one of them is already a girl, 1/3 chance the other will also be a girl (GG)

You're assuming that each of those possibilities are equally likely, which they aren't. I don't know how much it affects the numbers, but statistically there are slightly more males conceived than females. Also, there are a certain percentage that are neither male nor female.

Paedantic Basterd · 03-04-2013, 10:50 PM

I see.

The question we're being asked is about the odds of two disjoint events occurring together (Girl 1 followed by Girl 2), not the probability of a single event (the birth of either a boy or a girl).

I'm not sure if we can assume that biologically, inheritance of the X or Y is an even 50/50 split, since more women are born in the world than men, but I see where this is going.

**Janszoon** · 03-04-2013, 10:53 PM

Quote:

Originally Posted by Pedestrian

I see.

The question we're being asked is about the odds of two disjoint events occurring together (Girl 1 followed by Girl 2), not the probability of a single event (the birth of either a boy or a girl).

I'm not sure if we can assume that biologically, inheritance of the X or Y is an even 50/50 split, since more women are born in the world than men, but I see where this is going.

I think it's the reverse actually, as I mentioned above. Either way the point still stands that it's not 50/50.

Paedantic Basterd · 03-04-2013, 10:54 PM

It's entirely possible I'm incorrect, but I do believe I recently covered this in my studies somewhere.

Anyone else want to weigh in?

**Janszoon** · 03-04-2013, 10:58 PM

Quote:

Originally Posted by Pedestrian

It's entirely possible I'm incorrect, but I do believe I recently covered this in my studies somewhere.

Anyone else want to weigh in?

I think there are more women in the world than men, because women have a longer life expectancy, but when it comes to babies I believe there are males than females.

According to Wikipedia:

Quote:

In 2010, the global sex ratio was 986 females per 1,000 males and trended to reduce to 984 in 2011.

Paedantic Basterd · 03-04-2013, 11:01 PM

Oh, okay. Interesting, I sort of figured it'd be the other way around since there are more Xs kicking around in the gene pool than Ys. Wonder why that is.

**Janszoon** · 03-04-2013, 11:03 PM

Quote:

Originally Posted by Pedestrian

Oh, okay. Interesting, I sort of figured it'd be the other way around since there are more Xs kicking around in the gene pool than Ys. Wonder why that is.

I don't know. It is definitely weird.

Paedantic Basterd · 03-04-2013, 11:06 PM

Do those recorded births only take into account infants after a certain age, or is it possible that infantcide could make up the 14+ point difference?

This topic is piquing three of my academic interests at once.

Burning Down · 03-04-2013, 11:07 PM

Quote:

Originally Posted by Pedestrian

Oh, okay. Interesting, I sort of figured it'd be the other way around since there are more Xs kicking around in the gene pool than Ys. Wonder why that is.

That wouldn't determine the ratio of women to men though, since women are supposed to have two X chromosomes and men determine the gender of their children, so then there are only as many X sperm around as there are men in the world.

Paedantic Basterd · 03-04-2013, 11:08 PM

Quote:

Originally Posted by Burning Down

That wouldn't determine the ratio of women to men though, since women are supposed to have two X chromosomes and men determine the gender of their children, so then there are only as many X sperm around as there are men in the world.

Right, I didn't think that through.

View Poll Results: What are the chances the other is also a girl?
0%	1	9.09%
25%	0	0%
33%	4	36.36%
50%	5	45.45%
100%	1	9.09%
Voters: 11. You may not vote on this poll

03-04-2013, 10:50 PM	#32 (permalink)
Paedantic Basterd Music Addict Join Date: Sep 2010 Posts: 5,184	I see. The question we're being asked is about the odds of two disjoint events occurring together (Girl 1 followed by Girl 2), not the probability of a single event (the birth of either a boy or a girl). I'm not sure if we can assume that biologically, inheritance of the X or Y is an even 50/50 split, since more women are born in the world than men, but I see where this is going.

03-04-2013, 10:54 PM	#34 (permalink)
Paedantic Basterd Music Addict Join Date: Sep 2010 Posts: 5,184	It's entirely possible I'm incorrect, but I do believe I recently covered this in my studies somewhere. Anyone else want to weigh in?

03-04-2013, 11:01 PM	#36 (permalink)
Paedantic Basterd Music Addict Join Date: Sep 2010 Posts: 5,184	Oh, okay. Interesting, I sort of figured it'd be the other way around since there are more Xs kicking around in the gene pool than Ys. Wonder why that is.

03-04-2013, 11:06 PM	#38 (permalink)
Paedantic Basterd Music Addict Join Date: Sep 2010 Posts: 5,184	Do those recorded births only take into account infants after a certain age, or is it possible that infantcide could make up the 14+ point difference? This topic is piquing three of my academic interests at once.