G can never solve this, and this is why g will never make it

>muh 9000 genders

They're throwing in a ton of bad information to make you think about retarded shit you don't have to.

Odds don't change based on previous results it's literally not how they work. You can technically get a 1000 coinflips to be heads it's just very unlikely and calculating that statistic is more annoying than this one.

They are just asking you "What is the chance that a child will be born a boy?" and "what is the chance a child will be born a girl"?

>In most industrialized countries about 105 boys are born for every 100 girls, for a ratio of 1.05, known as the secondary sex ratio, or SSR; the primary sex ratio is the ratio at conception.

scientificamerican.com/article/is-a-pregnant-womans-chan/

Shitty source but that's correct

Honestly don't even care. I hope he just copy and pastes someone's answer, gets the homework right, and then fails the exam because he's a dummy who doesn't understand basic statistical probability.

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Are we supposed to assume that boys and girls are equally likely to be born in this household and that identical twins have a zero % possibility?

You're wrong in this one.
It's one of the cases where intuition is wrong, unless you studied probability.

The question as posed, has a sample space of:
GG GB BB (G=girl, B=boy).
The conditional probability of the second person being a boy, given the first is a girl, is:
P(GB)/P(G)= (1/3)/(1/2)=2/3.

That's completely arbitrary though. The gender of the first child has no affect on the reality of the second.

slam the fucking door in the little bitch's face and ask where the boy is then give him a high fucking five then go play ball with him

fuck all this subtle feminist brainwashin boys rule girls drool

>sees a girl open the door
>still somehow has BB as a possibility in his sample space

Lmao @ u r lyfe

Absolutely redpilled

have seggs

do you want to post this on every board user?

Nobody answers the door. I don't have hands to knock.

2/3 GG GB BG
he spams this from time to time, just wait for the golden ball nigger

50/50 for both. the probability of one occurance has no bearing on the probability of another.

the only time the likelyhood would be 1/4 is if you DIDNT know that the answering child is a girl, in which case there is four equally probable possibilities for combinations of children. otherwise, 50/50 in each instance.

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Btfo me if I'm wrong, but wouldn't it be 33%?

What part of
>Odds don't change based on previous results
do you not understand?

>It's one of the cases where intuition is wrong, unless you studied probability.
This is incorrect. The intuition of most people is to assume that the odds change when a previous result has been established. They do not. Unless for some reason the results are conditional on a previous result, which in this case they are not.

A boy being born, or a girl being born is an independent event that as far as we know are not related to each other. (technically they are because a man can produce more X or Y chromosome sperm depending on hormones and ballsack temp and a lot of other shit but we're ignoring that now)

I'm open to being wrong, i haven't studied probability formally. But I would like you to explain

The question isn't
>What is the chance of a person being a boy or a girl?
It's
>What is the chance a couple has a boy and a girl, given that one of them is a girl?
To better understand this, consider a family with 10 children. Picking one at random, you can say a given child has a 50% chance of being either male or female, but that doesn't mean the chance of all 10 being female is 50%.

>That's completely arbitrary though. The gender of the first child has no affect on the reality of the second.
It's not arbitrary. It's how conditional probability works. This is a basic assignment on every probability course. Essentially there's two rules you need to remember for all those assignments, conditional probability formula, and law of total probability.

Not sure if trolling or not, but the original sample space is of course all three possibilities, because the condition is not *yet* accounted.
The fact that the girl opened the door is accounted in the conditional probability formula.

>odds don't change based on previous results
so probability is wrong, the entire thing

I guess what they're trying to do is the old shit trick.
If a couple has two children they have four possible arrangements, these are in order of age.
BB, BG, GB, GG

If a G answers the door then BB is not a possibility, but you don't know if the G is the older or younger of the siblings, which means there are two out of three options where the second sibling can be a B.

In the second case BB and BG are not options, because a G is the oldest sibling, making it only a 50/50 chance the second sibling is a B

(i) 50%. Just because a daughter answers the door doesn't mean jack shit about the gender of the other child

(ii) theres 2 scenarios. This is the eldest in which case the other child has 50% being a boy. Or this is the youngest in which case the other child has 0% being a boy. So 25%?

i. P=0.5, we haven't met the other child, and we don't know the gender of them
ii. This is more complicated. We know there are two children, one is the oldest. We don't know who answered the door. Since we can assume each child is equally likely to answer the door, then we have a 50% chance the person answering the door is the eldest daughter. If it is the eldest daughter, then the other sibling (the younger sibling) has a 50% chance of being a boy, like before. However, if the person answering the door is not the eldest, then there is a 100% chance that the other child (the eldest) is a girl.
Therefore: P = (Chance answering is eldest)(Chance if boy if eldest answers) + (chance answering is youngest)(chance is boy if youngest answers)
P = (0.5)(0.5) + (0.5)(0)
P = 0.25 + 0
P = 0.25

BRAINLETS IN THIS THREAD

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1. 50%
2. 33%
Why?
1. it is clear it is 50%, just because it was a girl, it does not matter for the second child
2. The catch here is the word "eldest", so there is a difference between the cases where children open the doors.

if you just write the possiblities down you will get it

2.1 a girl opens - either it is the elder or the minor, if it is the elder, the other uses cases are 50%, but if it the minor, the other uses cases are 100% girl. so there are 3 pairs of possibilities - EG-MG (elder girl, minor girl) , EG-MB, MG-EG, the EG-MB is the 1/3 with boy in it.

Both questions are technically asking the same thing. Read them again carefully. The answer is 50/50.

>the absolute state of Jow Forums
I didn't even go to college or take probability in high school, but this is easy as fuck.

The first child is a loli, the second is undetermined, thus splitting the timeline into two timelines which are equally likely as of right now

>loli - loli
or
>loli - shota

Next, the door is opened, revealing a loli. This gives us more information as to which of the two timelines we're more likely to be in.

GIVEN we are in the double-loli timeline (LL), the door opening would reveal a loli 100% of the time.

GIVEN we are in the loli-shota timeline (LS), the door opening would reveal a shota 50% of the time

We now know we are twice as likely to be in the LL timeline versus the LS timeline. This means we have to have a 66.66% chance of being in the LL timeline than the LS timeline (33.33%)

And there is our answer. There is a 33.33% chance the second child is a shota.

Don't reply if you didn't get a perfect or near perfect score on your ACT.

>>Odds don't change based on previous results
>do you not understand?
It's not a previous result, it's a condition.
Conditional probability doesn't work like a known fact. What you're describing and you have in mind, is the second case, where you know already that one child is a girl. Then the second child is an independent event, not affected by that known fact.
Maybe the wording seems weird if you haven't studied this kind of problems. But case 1 and case 2 are different. Probability in case 1 is 2/3, in case 2 it's 1/2.

The explanation I can give you is, in case one, you don't know for sure if there is a girl, or a boy, until a person answers the door. So you have to keep all GG GB BB in your event space.
In case 2, you know that there is a girl for sure, so you have to discard BB from your event space. Then using the same formula you get 1/2.

I don't know what else I could say. I could give you a PDF from an introductory probability class (undergrad level). I didn't specialise in probability, but a couple basic classes are part of the curriculum for all math courses.

>i: 1/2
>ii: 1/3

>GG GB BB (G=girl, B=boy).
No, the sample space is GG, GB, BG, BB. There are two combinations where the children are of different genders, so it's twice as likely as them both being boys or both being girls.

I like how you are trying to find the cases where the loli and shota open the door. lol

>If you feel like the dumbest person in the room then you're in the correct room.
I honestly feel so incredibly stupid right now

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Yikes!

Math threads on Jow Forums are always like 25% trolling on purpose, 25%retards, 25 % people just talking out of their ass for no reason and 25 % smart anons providing correct answers and I can’t always tell who is who, including myself, except I’m probably not always part of the smart group.

EG-MG, EG-MB, and MG-EG do not all have equal probabilities, there is a 50% chance it is EG-MG/EG-MB and 50% chance it is MG-EG

The sample space is GG GB BG BB for one, so try again

>No, the sample space is GG, GB, BG, BB. There are two combinations where the children are of different genders, so it's twice as likely as them both being boys or both being girls.
This is the trick part of the question. GB and BG is a single (indistinguishable) event, because order doesn't matter. If the order mattered you'd be right.
Why do you think BG and GB is different? It's the same family with two kids, a boy and a girl.

What if they're non-binary?

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i: 50%
ii: 25%

>Why do you think BG and GB is different? It's the same family with two kids, a boy and a girl.
Because it's equally likely that the children are of differing genders as it is that they are of the same gender, whereas if you characterize the input space as BB, BG, GG, that would imply that them being the same gender is twice as likely as them being different.

>GB and BG is a single (indistinguishable) event, because order doesn't matter.
Order does matter, especially for the second question, because they are distinctly different. Either the girl is older and the boy is younger or the boy is older and the girl is younger.

Then you close the door.

When you have the first child you have a 50/50 chance of it being B or G. The second child then is a 50/50 chance meaning that you now have 4 possibilities: B followed by B, B followed by G, G followed by B, or G followed by G. i.e. BB, BG, GB, GG. BG and GB aren't a "single indistinguishable event" they're two equally likely but distinct possibilities.

Two kids
Girl answers door in both questions.
What is the likely hood of the other child being a boy in each scenario?
>HURRRRRRRRRRRRRRRRRRRR!!!!

This kind of intolerance is why women and non-binary people don't get into STEM.

>The first quarter landed on heads, the second is undetermined, this splitting the timeline into two timelines which are equally likely as of right now

>heads-heads
or
>heads-tails

Next, the quarter is flipped, revealing a heads. This gives us more information as to which of the two timelines we're more likely to be in.

GIVEN we are in the double-heads timeline (HH), the quarter flipping would reveal heads 100% of the time.

GIVEN we are in the heads-tails timeline (HT), the quarter flipping would reveal a tails 50% of the time

We now know we are twice as likely to be in the HH timeline versus the HT timeline. This means we have to have a 66.66% chance of being in the HH timeline than the HT timeline (33.33%)

And there is our answer. There is a 33.33% chance the second flip is tails.

Don't reply if you're a brainlet

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>everyone saying 50%
Is this some joke you're all in on or are you all that retarded?

They didn't ask about chance of all the children being girls, just one of them.
You fucking retard, conditional dosen't work like that. We NOW know that one child is a girl, therefor all other events are irrelevant. Now there is two possibilities: GB and GG. You have to normalise your chances so that in sum they would be equal 1.

>being this retarded
HAHAHAHAHHAHAHAHAHAHAHHAHAHAHAHHAHAHAAHHAHAHAHAHAHAHAHAHAHAHAHAHAHAHHAAHAHAHAHAHAHHAHAHAHAHHAHAHAHAHAHAHAHAHAHAHAHHAAHAAHHAAHAHAHAHHAHAHAHAHAHAHAAHAHHAHAHAHAHAAHHAHAHAHAHAHHAHAHAHAHHAHA

Before you answer the door:
P(GG) = 0.25
P(BB) = 0.25
P(BG) = 0.25
P(GB) = 0.25
so P(BG or GB) = 0.5

can't tell if serious or not

Is this an autism test?

>People carrying over their probability spaces when given new and relevant information

I put three guns on a table in front of you and inform you that one of them is loaded. I pick one up, squeeze the trigger, and nothing happens. I then ask you to pick up one of the remaining two guns and shoot yourself. What are the odds that you eat a bullet?

I don't close the door on women, though.

It’s 50/50 but someone’s going to come up with math autism to try and say different I bet

Listen up, brainlets. X = male, Y = female, uppercase answers the door.

In question one, there are eight possibilities to begin with: Xx, Xy, Yx, Yy, xX, xY, yX, yY. The condition "a daughter answers the door" eliminates half of these, and the four remaining are Yx Yy, xY, yY. Of these, in two cases the one not answering the door is a boy: Yx and xY. Thus, the probability is 2/4 = 1/2.

In question two, there are only four possible cases to begin with, given that the oldest child is a girl: Yy, Yx, yY, yX. Of these, the condition "a daughter answers the door" leaves three: Yy, Yx, yY. Of these, there is only one where the ony not answer the door is a boy: Yx. Therefore, the probability is 1/3.

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Actually I think since there is 100% chance the eldest is a girl it tilts the probability of whether or not the girl that answers is in fact the eldest. So it's not a simple 50/50

0%
Because I'm not going to point a gun at myself.

I SPECIFICALLY capitalized the word "given" so you fucking idiots would understand that this is not a coinflip scenario. We are being exposed to information about coinflips which have already occured, and due to the stiulation that one of those coinflips resulted in a girl being born, we find out we're more likely to be in a timeline in which both of the children are girls.

Your post doesn't even make sense. There are three coinflips in your post, because you can't understand that a stipulation is different than a coinflip. Go back to watching anime NEET.

In the second question, you are told the eldest kid is a girl, and she answers the door, it then only asks what the probability of the other kid being a boy is. Is the same god-damned question as the first, it just has some meaningless information thrown in.

Your systemic sexism closes the door also on other underprivileged gender groups.

>you are told the eldest kid is a girl, and she answers the door
No, you are told the eldest kid is a girl, and a girl answers the door.