Twins

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if you wanna take a quick peek...

Two babies are cute

>>8062204
If you had octouplets and knew that 7 of them are boys, would that make the eight an almost certain girl?
Stop your retardation right now.

>>8062234
What does your scenario have to do with my question?
Are you saying I was incorrect in assuming there being a 2/3 chance of having a girl after seeing the test results?

Why is it 67%? I don't know how chromosomes work in twins

>>8062204
nice thread OP

>>8062260
Each twin has 50/50 chance of either boy or girl.
So there's 4 scenarios-
BB
GB
BG
GG
We can eliminate that last one since that's not possible. In 2 out of the remaining 3, a girl is present. Hence in 67% of cases, I'm having a girl.

>>8062204
It's 50/50 now.

>>8062285
That was my initial thought as well right when I saw the sonogram image...
But the fact of the matter is that no NEW knowledge was gleaned from me seeing that image. I knew there was a boy in there. Help me understand why the probability shifted just from me seeing something I already knew.

>>8062259
I'm saying exactly that. Your chances dropped

>BB
>GB
>BG
>GG
>We can eliminate that last one since that's not possible

Actually you have to eliminate GG and GB, because child A is a boy. You are left with BB and BG.
50/50
Bye

>>8062302
well, there's a 50/50 chance you were looking at the boy you knew you had already, so that factors into it....

>>8062204
>So I knocked my wife up

It's ok, anon, we all know Tyrone knocked your wife up.

>>8062302
The way I see it, there's a tree: one branch where you saw child B, one where you saw child A (known from test). So, there's only one scenario if you saw child B: both are boys. With child A, there are still 3 scenarios, of which two result in a girl, and one results in a boy. So, the probability that both are boys is .5 + .5*.33333.... = 67%, one girl is 33%

>>8062302
That's not true, you gained knowledge of which child is guaranteed to be a boy.

>>8062307
Initially I had no idea which twin I was looking at. Are you saying that the probability would collapse only if I knew which twin I was looking at?

It's still 2/3
Here are your cases
BB saw left, B
BB saw right, B
GB saw left, G
GB saw right, B
BG saw left, B
BG saw right, G

4/6 = 2/3.

>>8062204
Everything is 50/50. It either happens or it doesn't happen.

>>8062322
The twin you are looking at is a specific twin. You seem to have a mistaken view of what "which twin" means.

>>8062328
You just calculated the chance of him seeing a boy, not the chance of the other child being a boy. We already know he saw a boy, and 2/4 times he sees a boy the other child is a boy.

>>8062333
Oh, right, haha. I don't know how i missed the entire point while writing that up. Thank you!

>>8062204
>thinly veiled Monty Hall thread
5/10 for effort and you've fooled some people.

>>8062344
It's almost exactly the Monty hall. Really happened though.
Punch line - both are boys.

Stale pasta

>>8062373
Nah homie. Shits for real

>>8062277
it's 75% you fucking retard

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>>8062204
>mfw some fucking story leads into a standard sci thread

>>8062367
>Really happened though.
If that's true, then how does this work:
>>8062204
>Since they aren't identical twins,

How did the doctors know they were fraternal twins?

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>>8062413
>Nah homie.
Lol, I read that as "Hah Normie" at first.
I spend too much time on this site.

>>8062277
>BG
>GB
please nobody fall for this bait

I remember when my sister was pregnant with my nephew...

I was standing in the room with her as they were doing the sonogram and she didn't know the sex yet, that's what they were trying to figure out. They got his little doodle on the screen and the technician froze the video and put a little yellow arrow pointing to it and said, "We have a boy!"

My brother-in-law said, "You could have made the arrow a little bigger." We all lol'd and a few months later my nephew was born.

RIP.

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>>8063438
>please nobody fall for this bait
If he's talking about the blood test, it's not bait.
If you'd rather say there are three possibilities, both boys, both girls or one each, you have to acknowledge that "one each" is twice as likely as either "both boys" or "both girls".
After eliminating "both girls", we still get 2/3 chance of at least one girl.

>>8062204
I'm afraid there's a 2/3 chance that one of them is going to be a goat. Sorry OP.

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>>8063431
We knew right from our first sonogram that they weren't identical.
With identical twins, you would not see a separation in the sac that they are in, however ours were in separate sacs so they must be fraternal.
Pic related. 3d sono pic from our first sonogram.

50%.
>Monty
Monty's problem was that you chose something with 33% chance of being correct then you are shown a goat which has no bearing on your chances, then you are given the choice of switching to something that is either a goat if you hit your 1 in 3 chance at the beginning or a car in other two cases.

Here you just know that from possibilities BB GB BG GG you are at BX and so the only two possibilities that can happen now are BG and BB giving BG 50% chance of happening.

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>>8062277
I actually laughed.
This board sometimes.

>>8063516
>you are at BX
Am I at BX if I don't know whether I'm looking at twin A or twin B? In that case I could be at BX or XB... leaving me still with BB, BG, and GB.
This goes back to my initial point which has been a bit derailed - When I walked into that sonogram it felt like the probability dropped to 50%, but in reality I was still at 67% until I knew which twin I was looking at. Is that accurate?

>>8062322
Of course it would collapse, the same way it would collapse after the birth once you know their sex.

>>8063487
Oh, thanks for the info.
And congrats on having kids, OP!

>>8063538
There is 50% chance you are at BX and have 50% chance girl so total 25% of it being BG.

There is 50% chance you are at XB and then you have either BB or GB to consider so girl with 50% chance. 25% total of it being GB

The choice is arbitrary. It all sums to 50%. Just think of it from the point of view of biology retard, why would a mother that has birthed 5 sons suddenly have a higher chance of girl being born.

>>8063538
>When I walked into that sonogram it felt like the probability dropped to 50%, but in reality I was still at 67% until I knew which twin I was looking at. Is that accurate?
No.

It's case of shit luck strike. It's what casinos make money with. Just because you fail in a luck game a lot doesn't mean your next victory is imminent.

>>8063552
>>8063555
Okay... imagine my wife swallowed two quarters - one red and one blue. The doctor has a blood test that will tell us if either or both landed heads. Test comes back positive for heads.
We don't know if the red or blue or both are heads. All we know is that at least one of them is heads.
We get a sonogram done, and on the screen we see a black and white image of a quarter that landed heads. We don't know if it's the red or blue one. So there's three possible scenarios left.
1. Red heads, blue tails
2. Blue heads, red tails
3. Red heads, blue heads.
Each of those are equally likely still. And two of the three contain tails. How am I wrong?

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>>8062204
>this thread again
OP, please.

>>8062204
COPY PASTA

>>8062204

A cell-free fetal DNA test would be able to tell you if you're having two boys or one girl and one boy. The test relies on the relative amounts of chromosomal DNA floating around in the blood of the mother.

If both were boys, the relative amount of Y chromosomal DNA would be consistent to that in a woman who was undergoing a single (male) pregnancy. If one of the fetuses is female, the Y chromosomal fraction would be halved relative to the single male case, as the total amount of non-Y DNA is essentially doubled.

Down syndrome is detected by discovering an extra 50% more chromosome 21 DNA relative to what is expected in a normal fetus.