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

What are the chances the other is also a girl?

I am gonna go out on a limb and say 50%.

I'm gonna go out on a limb and say vote :wave:

Assuming that the chance that the father will supply an X or a Y chromosome is equal (i/e, 50/50) then 50%. Why did you say 33%, Tuna?

I'm going to wait for a few more responses before explaining my position :)

Not that I think it would matter a whole lot, but do the kids have the same father? I read once during an anthropology class that if a couple has one child, subsequent children are more likely to be of the same gender as the first child. This theory wouldn't apply if the children had different fathers, because it's something to do with the process of meiosis in the man's body, and every man is different.

Same father: I'll say 66% more likely that the other child is also a girl. Not a poll option but I could add it for you if you want. (You already have 33% up there.)

Different father: 50% or less.

If the two kids are identical twins, then I guess the answer would be 100%.

If I know math; which I don't; then the answer is 42.

Damn. You edited your post before I could reply to it, lol

Haha! But, really, the whole world is girls.

The probability is completely independent of whether or not the first child is a boy. When you toss a coin 99 times and get 99 heads, the probability of the next toss being a head is still 50%. However the chances of getting 100 heads in a row in the first place are very low.

Don't think there are any other biological factors to worry about here, the fertilised egg has even chances of gotting a Y chomosome as it has of not getting it.

I'm a lady?

I'm going to say that at first, it's 50% that it's a girl. But you've already said one is a girl. Now, intuitively I want to say that it's obviously not 100% that the other kid is a boy, obviously. But I don't think you halve the remaining 50% for the next child either, so I went with 33%.
I wish I could justify my answer better. But all I have is that it seems like it's in between 50 and 25 for me.

Yep same father

Yep.

Okay yeah, my vote stands at 66% likely that the second child is also female. It's a trend that I've also noticed with people that I know - a lot of them who have siblings tend to have more siblings of one gender then the other.

Finally. Now I can be fabulous.

I chose 100% for fun. It's all about probability but in this case also biology.

Gotta be 50%. I asked Yahoo.

Ok two things:

1.) As Vanilla said, the emphasis is on probability and biology, but moreso probability.

2.) It's a counterintuitive problem.

congrats on another horrible thread.

I'm too lazy to go and look, but I'm pretty sure I heard that there is a higher percentage of females to males. Which would make sense if we evolved to live in groups led by one dominant male who mated with a large number of females. Having as many males as females might be a waste of resources. Of course there isn't an option for a higher chance of it being a girl besides 100%, so I choose anal beads. And since that isn't an option, I refuse to vote out of protest.

If anything it should be slightly higher than 50%. If they are twins then they're more likely to be the same sex. So 51%. Picked 50. And any gender variation such as asexual/haemophrodite/statistical variations like slight changes in birthrates thrown in wouldn't tip it more than 5% either way.

Especially since the scenario doesn't outline if the known girl is the younger or older sibling

i'm going to say 33% because if it's a boy, natural selection has created a group ratio of 2:1. it seems to me that there needs to be more women because birthing is a longer process than f*cking. and i have no other input on this other than to say i deduced it from a beach boys song.

:rofl:

It's a trick question. She's barren.

50%. She'll either have a boy or a girl.

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)

I'm not sure if I understand this logic. Are you trying to use the Punnett square technique to determine sex? Because then all four choices would still apply for subsequent children.

I think you and me are making the most threads lately! I go through phases of thread ideas. But yeah MB is just as good now as it was before. However people are a lot more whiney these days, including me!

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.

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.

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:

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.

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.

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.