So my wife and I are having twins. Two weeks ago the doc drew

>>7937272
This has to be an elaborate troll

There is at least one boy
No information on the other kid = it's as if you had two separate kids but you didn't do any blood test for the second one.

>>7937292
This has to be a blatant troll

3 options
Boy boy
Boy girl
Girl boy

So 2/3th chance it's a girl

>>7937292
>>7937304
no troll.
The way I see it, there are 4 possible outcomes with baby A & B -
A = girl, B = girl
A = boy, B = girl
A = girl, B = boy
A = boy, B = boy
So right off the bat we can eliminate the top one. We know that ain't happening. That leaves three possibilities. In two of those three, we are having a girl. So 2/3 chance of the other baby being a girl instead of 50/50.

Is this the wrong way of thinking about it?

>>7937307
That's exactly what I (>>7937304) said

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>>7937272
and fifth possible outcome is, a hermaphrodite.

>>7937311
shit. I should read.
Doctor didn't know what she was talking about. Thanks for confirming.

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>>7937315
at least not a horned human, thanks god.

>>7937315
extremely unlikely, and usually it comes paired with other birth defects that they would have detected

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>>7937321
>hermaphroditism
>other birth defects
>OTHER
God damn you! Equality of genders!

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A boy, or an abortion?

So 100-0 chance, boy.

>>7937272
Actually you don't know what either of them will be because you don't know what they will identify as.

>>7937272
We forget though anons, we must take into account the likelihood of identical twins.

after you factor in this, our answer will become slightly more unclear.

>>7938031
That's pretty easy to tell. They're not identical. Dizygotic.

>>7937272
on its own the other child has a 0.5 chance of being either sex .
options before: BB,GG,GB,BG, as there's no significance to their order its 0.5 BG and 0.25 GG\BB.
options after , at least one B: BB,GB,BG . 2/3 its a GB and 1/3 its BB.

probability of certain result = all the possibilities that match it / all possibilities
that is assuming equal chances in each child and non dependence of one on the other , which is roughly correct in this case within a margin of error no bigger then ~0.05.

OP you correctly identified a monty hall type situation

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>>7937304
>boy girl
>girl boy

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>>7938055
confirmed for now knowing shit about probability .
i feel bad for you man .

>>7937272
did you come up with this variant of the problem?
because i think it's brilliant
it introduces the randomness necessary for the 2/3 solution in a realistic and really unambiguous way

>>7938062
?????
the twins are in a superposition state until they are observed.

We know one of them is a boy, but the other is either a boy or a girl so until observation, it is both with a coefficient of 1/sqrt(2) for each possibility.

>>7938068
if i do pairs of coin flips ill get 0.5 of them landing on different sides and 0.25 each of both landing on same side , if i disregard all the outcomes within one of those 0.25 i get 1/3 of both one side and 2/ of both different sides .

you can literally try it with a coin and see .

>>7938066
This is actually a real scenario that my wife and I are in. We already have a 3 year old boy and were hoping for a girl. When we found out that there were fraternal twins, we were really hopeful. If they were identical, it would just be 1/2 chance of girl, but since they were fraternal 3/4 chance of girl.
When the doc told us about the boy and 50/50 chance of the other being a girl, I thought it sounded wrong based on two factors - my prior calculation of 3/4 chances of getting a girl and reading about the monty hall problem. This seemed like the exact same type of probability problem. I feel like this is something the doctor / lab may encounter every so often, so they should be a bit more accurate with their communicating of the probabilities of the possibly outcome.

>>7937772
>Actually you don't know what either of them will be because you don't know what they will identify as.
Obvious troll, but if taken seriously, it hardly changes anything since there's only a 1% of them cross-gender identifying.
AND just over 51% of newborns are male (not counting China), so there's that too.

>>7938032
>They're not identical. Dizygotic.
Out of curiosity, how is this determined?

>>7938062
well even the smartest do have a couple of brain farts now and then if they ever have an original thought.

>>7938075
shouldn't it be a 1/4, 3/4 split ?
but i guess the whole thing hinges on whether or not the order is important.Im not sure if it should apply to the babies because gb and bg are indistinguishable. i think this situation is more analgous to flipping two coins, but one has heads on both sides but you just dont know which one.

>>7938080
>3/4 chance of girl
I'm sure it's 2/3.

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>>7938095
It's determined visually with an ultrasound. This is an image from our first ultrasound when we found out that we were having twins. With dizygotic there is a clear barrier between them and with monozygotic there would be no such barrier.
We both thought the sono tech was just fucking with us when she asked "do twins run in your family?" Until we saw for ourselves.

>>7938108
I was referring to the chances before the outcome of the blood test was known.

No, it's half. You know that one is a boy for sure. So it's 50/50 chance the other baby it a girl.

>>7937272
Nice thread OP, usually with this puzzle people say "it boils down to how you word/interpret it" but in this case it should be clear.

>implying you can determine a gender based on chromosomes and genitals
When they grow up ask them what "gender" they identify with.
Simple

>>7938139
Except we don't know which one is a boy. If they could definitively say that baby A is a boy, then you'd be right.
But they don't know if the Y chromosome came from A or B or both. They just know that a Y chromosome is present in my wife's blood.

>>7937272
1/2 chance the *other* child is a boy. 1/3 chance *they* are both boys.

>>7938176
Call the confirmed boy "baby A".
Enjoy.

>>7938176
We don't have to know which is a boy because the question is asking about the "other child".

>>7938216
>>7938223
Actually I'm going to change my answer to "the question does not make sense", because it is unclear what "the other one" refers to. When we say that at least one is a boy, this is a statement about the two babies as a set. not about one particular child, unless the test detects a unique Y chromosome and doesn't just tell you "there are Y chromosomes in the blood". The latter is more likely I suspect. The doctor is wrong but not because he screwed up the probability, but because there is no "other one".

>>7937272
>friend is preggo and has the same test done
>doc says it is a retard and she should abort (test is repeated 3 more times with same results)
>she waffles about it for a long time
>decides not to abort
>kid is 15 now and not at all a retard, best in his class

The more I live life the more I doubt just about every fucking thing there is anymore.

>>7938237
Cell-free fetal DNA testing was developed in 2007 and publicly available around 2011. If that kid is 15 it wasn't the same type of test.

>implying biology determines gender

>>7938307
So you're saying people just choose their gender based on environment and not how they're born? Do you think gay people choose to be gay as well?

>>7938315
I'm pretty sure that prenatal environment is considered to be the primary factor in sexual orientation. Not the ONLY factor, mind you.
Now gender may be different, and I'm quite sure biology plays a role... But probably not in the definitive way that some think.

>>7938263
True, I have no clue what test it was other than, "a test to see if it was retarded or not."

However, whatever test it was, was accepted at that time and medical advice was to terminate the pregnancy. Thus, everything is still suspect.

>>7937272
Wait, think it this way.
>you detected the first one is a male
The second has 50% chance of being male
>you detected the second one is mele
The first has 50% of being male

>>7938378
You did neither, you only know the pair contains a male, not which is male. The question as it is asked doesn't make sense because there is no "other child".

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I've made some tests. Turns out ermaphrodites are more rare than previously thought

>>7937272

Leaving aside the boy/girl variant troll, there's something more important to discuss. You should know OP, that you wife is going to miscarry.

>>7938378
This. This is the correct way of approaching this kind of problem.

You know ONE is a boy. Options:

1) The first is a boy: BG, BB (50% chance of second being a boy)
2) The second is a boy: GB, BB (50% chance of first being a boy)

You have a 50% chance of option 1 being the correct scenario and 50% option 2 is correct. You therefor have:

50%*50% + 50%*50% = 25%*25% = 50%

Options 1 and 2 cannot coexist, so everyone saying that your options are "BB, BG, or GB so 2/3" is wrong.

News from medicine: It comes down to the question of identical twins or not. Usually 2/3 of all twin pregnancies are non-identical, meaning he chance is 50:50 here. For the remaining 1/3 of identical twins, the chance is 100:0 for a boy.

So 1/3*1 + 2/3*0,5 = 2/3 chance for a boy, 1/3 for a girl

>>7938584
She just entered second trimester. Miscarriage is less likely. Now preterm birth is highly likely with twins so I'm guessing that's gonna happen.
>>7938609
Why do you say option 1 and 2 cannot coexist? Can't they both be boys? If so, doesn't that mean option 1 and 2 coexist?
>>7938611
The twins aren't identical. I posted the sonogram pic earlier and it's clear to see they are dizygotic.

>>7938609
>1) The first is a boy: BG, BB (50% chance of second being a boy)
>2) The second is a boy: GB, BB (50% chance of first being a boy)
>You have a 50% chance of option 1 being the correct scenario and 50% option 2 is correct.
Your mistake is here. It is actually a 2/3 chance that the first child is a boy and a 2/3 chance that the second child is a boy, not 50%. That's because given the information there are three equally likely possibilities:

BG, GB, BB

2/3 of those have the first child as a boy. 2/3 have the second child as a boy.

>Options 1 and 2 cannot coexist, so everyone saying that your options are "BB, BG, or GB so 2/3" is wrong.
Of course they can coexist. If both children are boys then both option 1 and option 2 are true.

>>7938609
lel no
>>7938390

>>7938638
What do you think of my answer that the question doesn't make sense? There is no child indicated to be a boy so there is no "other one" to ask about. The doctor is not wrong because he got probability wrong, he's wrong because he asked a nonsense question.

>>7937272
>like that Monty Hall problem

>>7938611
Uh, no. If we approach the question from this angle, there are 5 possible scenarios:
1. Non-identical, 2 boys: 1/6
2. Non-identical, 1 boy 1 girl: 1/3
3. Non-identical, 2 girls: 1/6
4. Identical, 2 boys: 1/6
5. Identical, 2 girls: 1/6

Since one of the babies is a boy, it reduces to possibilities 1, 2, and 4. Which would give 50% chance of having a baby girl.

But it's a moot point anyway since the twins aren't identical.

>>7938643
If the question was phrased as something like "what is the chance of OP having a girl" then would the question makes sense?

>>7938638
>>7938641
The scenarios are mutually exclusive. Only one of those scenarios is possible. The fact that those scenarios contain one of the same outcomes is irrelevant ("scenario" may have been the wrong choice of word to express that, but forrealzs use your head).

Did nobody in this stats bait thread actually take stats? Mutually exclusive events, bruh.

>>7938643
I agree. The doctor worded her statement improperly.

>>7938646
>If the question was phrased as something like "what is the chance of OP having a girl" then would the question makes sense?
Of course.

>>7938609
>You know ONE is a boy.
Okay you can't read at all.

>If they detected a Y chromosome then there's at least one boy
>at least

>>7938649
>The scenarios are mutually exclusive.
How are BB and BB exclusive? They are the same thing. So these events are not exclusive, they overlap.

>>7938644
Exactly! Except for the small fact that it's not like that at all.

>>7938658
Which is why they are in two different scenarios.

>>7938654
You DO only KNOW one is a boy. I didn't say that both can't be boys. Can you read?

>>7938666
>Which is why they are in two different scenarios.
...which overlap. They are not separate specifically because they include the same event.

>>7938666
The problem is that you're assuming that the detector will detect only one or the other, and it just so happens to return a Y chromosome. That is NOT what's going on here. The detector checked both, and returned a Y chromosome, which means that at least one of them is a boy.

>>7938669
Since they're non identical, this is equivalent to flipping two coins (assuming chances of boy/girl really are exactly 50%):

Two coins are on the table. You flip the first one. It's heads. Knowing that now, what is the chance that when you flip the second coin, it will be heads? Obviously it's 50/50.

If we asked "what are the chances of 1 head, 1 tail when we flip both coins" you'd say 50/50. If we then said "what are the chances of 1 head 1 tails if we force 1 to be heads?" you'd say 2/3. But that's not what we're saying. We're asking "now that we've flipped the first coin, what is the second coin going to be?"

That's where your confusion is coming from in this problem.

>>7938676
That's not what I assumed at all. These are just two scenarios which model the problem in a somewhat mathematical way. The logical way of thinking of it is: >>7938677.

>>7938666
My wife swallowed a nickel and a quarter. The doctors did a blood test and we were able to determine that at least one coin landed heads. We don't know which one landed heads...

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>>7938677
>We're asking "now that we've flipped the first coin, what is the second coin going to be?"
'no'

>>7938681
As expected in 3/4 of the outcomes. Now there are 3 outcomes left, with two of them having one be tails.

>>7938677
Your analogy fails because you don't know which child is male. Either could be male and either could be female. Either coin could be heads and either could be tails.

Here is the correct analogy: You flip two coins and ask your friend to tell if there is at least one head. He says yes. What is the chance both coins are heads? 1/3, because he either saw TH, HT, or HH, and these are all equally likely to have occurred. There is no "forcing a coin to be heads", it's just simple conditional probability.

>>7938684
>That's where your confusion is coming from in this problem.

'yes.'

The outcome of the first coin does not change the outcome of our subsequent coin, since the outcome of each coin is mutually exclusive.

>>7938692
You don't know the outcome of the first child, so this is an irrelevant statement.

>>7938691
But it doesn't matter which child is male. The "other" child, doesn't matter which, has a 50% chance of being male. He didn't ask us to specify which one would pop out first.

>>7938692
>The outcome of the first coin
See, you're already assuming >>7938676.

>>7938699
>>7938692
Word. The outcome is not necessarily the first coin. It could be the outcome of the second coin.

OP is right, doctor is wrong.

>>7938701
>But it doesn't matter which child is male. The "other" child, doesn't matter which, has a 50% chance of being male.
There is no "other child" because the test result doesn't tell us anything about a specific, it tells us about the set of children. That's what I've explained from the start. It's very simple and you have no way to refute this:

BG, GB, BB

1/3 chance of both being boys.

>>7937272

50/50 sounds right to me OP.
Consider the following.
A person has flipped a coin twice.
They tell you that on at least one of the flips, a heads was obtained.
There is still a 50/50 chance that the other flip also resulted in a heads.
The first flip has no bearing on the second flip.

>>7938709
Okay, so let's say the order of children is irrelevant.
The possibilities for genders are these UNORDERED sets:
BB,GG,BG with possibilities 0.25, 0.25, 0.5

We can remove GG because we know the set contains at least one boy, leaving us with BB and BG.
We have to normalize their old probabilities to get their current probabilities:
BB: 0.25/0.75 = 1/3
BG: 0.5/0.75 = 2/3

Now we see that 2/3 is correct and modeling this with unordered sets was retarded, because it would have been more obvious with ordered sets.

>>7938792
>Okay, so let's say the order of children is irrelevant.
The order of children has always been irrelevant. I only said first and second child to distinguish them since they are separate entities. "First" and "second" don't actually mean anything physical, neither does the order of BG or GB.

>Now we see that 2/3 is correct and modeling this with unordered sets was retarded, because it would have been more obvious with ordered sets.
LOL, thanks for the kek.

>>7938791
Stop samefagging you retard.

I think any biologically-based bias should really be considered here - this is not a probability for a purely random event.

>>7938095
Maternal DNA will differ if it's dizygotic. It won't if it's monozygotic.

>>7938880
I assume they didn't do DNA tests otherwise they would know the sex of both twins.

>>7938859
op here. I don't know which biological variable you're wanting to use, but here's the facts - She was near the end of her ovulation when I impregnated her, she orgasmed before I did, I orgasmed in doggy style. My father had two boys and zero girls. His brother had three boys and zero girls. My grandfather on my father's side had three boys and one girl. My wife's BMI is 17.5. Literally ALL of those things are assumed to lean HEAVILY on the side of my offspring being male.

However, I don't think there's any conclusive proof that any of those things matter. It is theorized that there is a gene that determines whether a man's sperm contains more x chromosomes or more y chromosomes, but that gene has yet to be discovered.

Either way for the sake of this probability exercise we are all assuming chances of boy/girl are the exact same as heads/tails.

>>7938896
Did you engage in oral sex beforehand? This is important. It would probably be best to provide photographical evidence.

>>7938896
>she orgasmed before I did, I orgasmed in doggy style.
How much did both of you enjoy it?
Rate it on a scale from 0 to 10, then multiply the result of you and your wife.
Th result will be a enjoyment correlation factor in the intervall [0,100].
The higher this factor, the higher the chance of getting a girl.
Since you already know she gets at least one boy, we can assume that the enjoyment correlation factor is below 50.

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>>7938926
>>7938929

>>7938926
Yes, but it was rushed. This was over the Christmas break and we were staying with her parents. They took our son out for dinner and we literally didn't have much time at all. We took advantage of the alone time, but didn't fuck around with extended foreplay. Didn't document the event this time. Sorry.
>>7938929
An orgasm is an orgasm. Honestly it was only memorable because of the fact that we were in a novel location. The sex was 5/10 for both of us.

>>7938963
>The sex was 5/10 for both of us.
that makes the enjoyment correlation factor 25.
This clearly proves that you have a 25% chance of getting a girl.