A man has two children. One of them is a boy.

halbpro · Oct 1, 2015

Moshe Gariani said:
Hans, with all due respect (i.e. none at all..!), this is nonsense. How on earth is b/g a different outcome to g/b when you are not worried about the order...?

I was following with HKFC, but you've torn my world asunder here. You're right, at least I think so. Girl/boy and boy/girl are of course identical if you don't care about which is the older sibling.

So you do start with:

1. Boy/boy
2. Boy/girl
3. Girl/boy
4. Girl/girl

And you have a roughly 25% chance of each. By stating one of them is a boy you eliminate 4, and as you don't care about which sibling is which you combine 2 and 3 down to a single option, leaving you with a simple 50/50 chance.

Now does the order matter? If you were to say "The older sibling is a boy" then you can again eliminate option 4, and while you can't combine 2 and 3 you can eliminate 3 because the older sibling (the first one) is a girl. So you're still left with 50/50.

Diablo · Oct 1, 2015

halbpro said:
I was following with HKFC, but you've torn my world asunder here. You're right, at least I think so. Girl/boy and boy/girl are of course identical if you don't care about which is the older sibling.

So you do start with:

1. Boy/boy
2. Boy/girl
3. Girl/boy
4. Girl/girl

And you have a roughly 25% chance of each. By stating one of them is a boy you eliminate 4, and as you don't care about which sibling is which you combine 2 and 3 down to a single option, leaving you with a simple 50/50 chance.

Now does the order matter? If you were to say "The older sibling is a boy" then you can again eliminate option 4, and while you can't combine 2 and 3 you can eliminate 3 because the older sibling (the first one) is a girl. So you're still left with 50/50.

WTF are you serious.............

halbpro · Oct 1, 2015

Diablo said:
WTF are you serious.............

I'm serious in my answer to this particular line of reasoning. I won't commit any further than that.

hans kraay fan club · Oct 1, 2015

halbpro said:
I was following with HKFC, but you've torn my world asunder here. You're right, at least I think so. Girl/boy and boy/girl are of course identical if you don't care about which is the older sibling.

So you do start with:

1. Boy/boy
2. Boy/girl
3. Girl/boy
4. Girl/girl

And you have a roughly 25% chance of each. By stating one of them is a boy you eliminate 4, and as you don't care about which sibling is which you combine 2 and 3 down to a single option, leaving you with a simple 50/50 chance.

Now does the order matter? If you were to say "The older sibling is a boy" then you can again eliminate option 4, and while you can't combine 2 and 3 you can eliminate 3 because the older sibling (the first one) is a girl. So you're still left with 50/50.

A man has two coins. He decides to spin both.

Question
"What is probability of both landing on heads"
Answer
25%. Only one of four possible outcomes is heads/heads.

Or would you 'combine' the h/t and the t/h possibilities into one, and call it 1 in 3 possibilities? No, you wouldn't.

Diablo · Oct 1, 2015

halbpro said:
I'm serious in my answer to this particular line of reasoning. I won't commit any further than that.

I`ve got three children two of whom are boys...is this ambiguous or can you work out that my third is................................................................a girl.

GingerBeerMan · Oct 1, 2015

halbpro said:
I was following with HKFC, but you've torn my world asunder here. You're right, at least I think so. Girl/boy and boy/girl are of course identical if you don't care about which is the older sibling.

So you do start with:

1. Boy/boy
2. Boy/girl
3. Girl/boy
4. Girl/girl

And you have a roughly 25% chance of each. By stating one of them is a boy you eliminate 4, and as you don't care about which sibling is which you combine 2 and 3 down to a single option, leaving you with a simple 50/50 chance.

Now does the order matter? If you were to say "The older sibling is a boy" then you can again eliminate option 4, and while you can't combine 2 and 3 you can eliminate 3 because the older sibling (the first one) is a girl. So you're still left with 50/50.

You can't just 'combine it down to 50%'. Think of 100 families with a distribution such that 25% have 2 two girls, 25% have a boy and a boy, 25% have a girl and a boy and 25% have two boys. The question says at least one child is a boy, so now it's 33% for BG, BB and GB. Obviously the age of sibling isn't stated so we can add GB and BG together because they're essentially the same, so it's 66% for GB/BG, but as we already knew the first was a boy it means there is a 66% chance the other is a girl, hence 33% the other is a boy.

A similar argument can be put forward for 50% but I have no battery left, hopefully I can get it out later.

halbpro · Oct 1, 2015

hans kraay fan club said:
A man has two coins. He decides to spin both.

Question
"What is probability of both landing on heads"
Answer
25%. Only one of four possible outcomes is heads/heads.

Or would you 'combine' the h/t and the t/h possibilities into one, and call it 1 in 3 possibilities? No, you wouldn't.

You can combine them if you know the answer to one though surely? Are we talking about a difference between flipping a coin twice and flipping two coins at the same time?

Moshe Gariani · Oct 1, 2015

hans kraay fan club said:
A man has two coins. He decides to spin both.

Question
"What is probability of both landing on heads"
Answer
25%. Only one of four possible outcomes is heads/heads.

Or would you 'combine' the h/t and the t/h possibilities into one, and call it 1 in 3 possibilities? No, you wouldn't.

What is the capital of Kenya?

halbpro · Oct 1, 2015

Moshe Gariani said:
What is the capital of Kenya?

Easy! K

pastafarian · Oct 1, 2015

Hello,how many children do you have?
I have two children,one is a boy
Ah a boy and a girl lucky you
Actually the other one is a boy as well
so you have two children and both are boys
yes
why didn’t you say that then
I don’t have to be specific from the outset
you are a dick

Diablo · Oct 1, 2015

moshe gariani said:
what is the capital of kenya?

i bor ian :lolol:

Goldstone1976 · Oct 1, 2015

Is the boy a Syrian, Islamic refugee?

We need a broader cross section of NSC opinion on this important topic - I'm hoping that the judicious use of certain key words in this post will draw in the NSC intelligentsia.

halbpro · Oct 1, 2015

Diablo said:
I`ve got three children two of whom are boys...is this ambiguous or can you work out that my third is................................................................a girl.

There's a difference between my answer to the question and my thoughts on a particular line of reasoning.

hans kraay fan club · Oct 1, 2015

halbpro said:
You can combine them if you know the answer to one though surely? Are we talking about a difference between flipping a coin twice and flipping two coins at the same time?

But in the original question we don't know the answer to either. We know that one is a boy, but not which one. Most are choosing to read it as 'there is a boy, what is the probability of THE OTHER being a boy', which is absolutely 50%. However the question doesn't say that. It says at least one is a boy. Either could be that one, which is why you can't 'combine' the two possible b+g outcomes.

halbpro · Oct 1, 2015

hans kraay fan club said:
But in the original question we don't know the answer to either. We know that one is a boy, but not which one. Most are choosing to read it as 'there is a boy, what is the probability of THE OTHER being a boy', which is absolutely 50%. However the question doesn't say that. It says at least one is a boy. Either could be that one, which is why you can't 'combine' the two possible b+g outcomes.

Ok, you've swung me back for now. I'm very fickle.

Moshe Gariani · Oct 1, 2015

GingerBeerMan said:
You can't just 'combine it down to 50%'. Think of 100 families with a distribution such that 25% have 2 two girls, 25% have a boy and a girl, 25% have a girl and a boy and 25% have two boys. The question says at least one child is a boy, so now it's 33% for BG, BB and GB. Obviously the age of sibling isn't stated so we can add GB and BG together because they're essentially the same, so it's 66% for GB/BG, but as we already knew the first was a boy it means there is a 66% chance the other is a girl, hence 33% the other is a boy.

A similar argument can be put forward for 50% but I have no battery left, hopefully I can get it out later.

This reminds me of Mrs Pepperpot calculating daily hours of activity.

We are not working with your chosen distribution as the distribution under discussion categorically does not include any possibility of the outcome being two girls.

In this distribution 50% have two boys and 50% have one of each.

Triggaaar · Oct 1, 2015

Moshe Gariani said:
There is limited or no REAL ambiguity in the original question. He found out one is male because I clearly told him in the question. I don't see how this reworded question is different.

I think it matters. This is why.

Easy part 1:
Let's consider 100 couples have a baby. Half have a boy, half have a girl.
Now let's consider they all have a second baby, half having a boy, half a girl.

Hopefully most of us would agree that 25% have 2 boys, 25% have 2 girls, and 50% have one of each.

Easy part 2:
If I walked up to a random couple and said 'do you have a boy, yes or no?' and they said yes, then the chances of their other child being a boy would be 1 in 3 (because 75% of the couples would have said yes, and of those, 1 in 3 (25% of total) would have a second and 2 in 3 (50% of total) would have a girl.

But the point is, I didn't find out by walking up to one of the couples and asking a specific question. That's not what happened, so I can't make the same deductions.

Difficult part:
A random couple was chosen from the 100, and a random gender was told to me.
Say we ran this test 100 times, and each couple was chosen once. For the 25 couples with 2 girls, I'd be told one was a girl. For the 25 with 2 boys I'd be told one was a boy. For the 50 couple with one of each, 25 times I'd be told one was a girl and 25 times I'd be told one was a boy.
So on 50 occasions I'd be told one was a boy. In 25 of those cases, the other would be a girl, and in 25 of those case one would be a boy.

It's 50%!

AlbionPics&SouthCoastTwit · Oct 1, 2015

pastafarian said:
Hello,how many children do you have?
I have two children,one is a boy
Ah a boy and a girl lucky you
Actually the other one is a boy as well
so you have two children and both are boys
yes
why didn’t you say that then
I don’t have to be specific from the outset
you are a dick

What percentage of conversations have these kind of misunderstandings? Or is this question too ambigious?

hans kraay fan club · Oct 1, 2015

Moshe Gariani said:
This reminds me of Mrs Pepperpot calculating daily hours of activity.

We are not working with your chosen distribution as the distribution under discussion categorically does not include any possibility of the outcome being two girls.

In this distribution 50% have two boys and 50% have one of each.

Let's run with this.

Do you think (in general, rather than within the confines of this question), there is the SAME probability of a two-child family having two boys, as there is they'll end up with one of each?

fat old seagull · Oct 1, 2015

I've given myself a feckin migraine just reading the complexities of this thread, much of which I don't understand. The one input I am able to offer is...I have two boys, and neither of them are Ronnie Pickering!

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