The boy-girl puzzle

Two kids, you know the sex of one. How many does that leave whose sex you don’t know?

2

What is the sex of the eldest child?… don’t know
What is the sex of the youngest child?… don’t know

3

What is the sex of the child with brown hair? Don’t know.

Y’know – I can’t help thinking that having a huge thread that continually uses the words “child” and “sex” might somehow attract the wrong sort of people using Google.

lol

The kind that posts pics of Stephanie from Lazy Town?

There’s a horse race with 6 horses:

Horse A will either win or lose – 50:50
Horse B will either win or lose – 50:50
Horse C will either win or lose – 50:50
Horse D will either win or lose – 50:50
Horse E will either win or lose – 50:50
Horse F will either win or lose – 50:50

(Won’t help the argument at all, but I wanted to add the word “horse” to the search mix.)

Well done mboy your question has sufficient info to work

I only threw the extra dimension in to add a touch of confusion to the situation for those that don’t understand, seems to have worked! 😉

Andy… but it doesn’t leave a single unknown, you are just making that assumption.

The question put by mboy, gives you three unknowns, but that third one is irrelevant. The original difference, birth order, is still there even without the race issue. You could just as well do it where one child has ginger and one child has blonde.

Yup, exactly, the 3rd unknown I created is totally irrelevant, I threw it in there to add confusion as stated above. It’s only the same as the Cat/Dog situation created slightly earlier on in this thread though.

Out of the 4 combinations you have all ruled out boy/boy.

That leaves

girl/boy
boy/girl
girl/girl

show me how to figure out the probability that the first one is a boy….

We might get ten pages after all!

Why do you want to know the probability that the first one is a boy?

Just want to know.

No answer to that one?

Boy Girl is, in this case, the same as girl boy. She has one girl, so the question may as well be “what are the chances that a woman’s first and only child is a boy?”

easy, 50/50 😆

…what are the chances of twins?

can’t be bothered to check but sometime back pointed out that the “rules” didn’t exclude the lady from being a liar – the result assumes she is telling the truth

Smee: from a population equally divided into GB, BG, GG – the chances of the “first” one being a boy are 1:2 aka 1 in 3 aka 33%.
Not sure how this is relevant to the question tho, or your cat’s arse and the sun.

Beveled Edge: no, you are pre-selecting. You don’t have that information at the start of the question. That is equivalent to saying that in the Monty Hall problem the host says “pick any door from these three, except that one.”

GrahamS – I didn’t ask anything about a population being equally divided between the three options. I asked what was the probability of the first child being a boy. Any answer other than 50:50 is obviously incorrect.

You didn’t state that, but it is vital information that we need to calculate the probability.

If we are still talking about the population in our problem then we have already established that it is equally split, so the answer is one third.

I have literally no idea how you can look at those 3 options and decide it is 50%

What does that mean the probabilty is for the second one being a boy???

Didn’t need to state it. The answer to the probability of the first child being a boy is only ever going to be 50% somehow you managed to come up with 33%. And you’re telling me that i’m wrong.

Probability of any other child being a boy is 50%

Right I think you have finally talked yourself into a corner. You say 50% so that means…

First child is a boy = 50%
Second child is a boy = 50%
Both are girls = 0%

Do you notice anything there?

If I am misinterpreting then please fill in your “correct” values.

Bear in mind that there is also a 50% chance that the first child is a girl – same as with any other child.

So your breakdown of the probabilities is….?

….is?

Well it seems to me it all hinges on whether boy/girl is the same as girl/boy. Under current discrimination laws we must not discriminate on sex or age and therefore we must assume boy/girl is the same as girl boy. Thus 50% seems to be the politically correct answer.

first child is a boy = 50%
second one is a boy = 50%
Both are girls = 50%

Because
first child is a boy = 50% it is a girl = 50% = 100%
second one is a boy = 50% it is a girl = 50% = 100%
Both are girls = 50% both are not girls = 50 % (as above)- there can be only two outcomes here two girls or boy /girl ORDER in this example is NOT a factor –

Don’t know or care whether any of this is correct just going for the 10 pages and will argue with you if it help GrahamS

Can I just add that I think both logic and maths answers are correct it is just like arguing over imperial verus metric measurements you get different answers but WITHIN their own system (following their own axioms) it is correct or true (which is not the same as TRUTH) so does it really matter?
Also think this is just a paradox as both (conflicting ) answers are correct
Surely given you enough options/ammunition now to continue the thread

He’s buggered off, makes a mess of trying to be clever again then tries to change what he meant in the question.

I went out on my bike. Got a puncture 20 odd miles from anywhere then ripped the valve off the spare tube.. Disco slippers are not great for walking in

What’s the odds of that!

Lets play 10 pages roulette. Is it this post that’ll get to 10 pages?

10 pages of you looking like an idiot? Works for me.

Blows kisses at nickc.

The only idiocy that is going on is people not realising that both solutions are correct…..

“boy girl puzzle” in google only gets STW to 2nd spot, more posts required 😉

Smee, play the devils advocate, try seeing it from the other side of the argument for a minute.

There is information you are assuming currently that does not actually exist, and there is also information that we do know that you are trying to ignore.

Smee – Member

The only idiocy that is going on is people not realising that both solutions are correct…..

Your solution is only correct if the children do not yet exist. Then of course the probability of the first child being a girl is 50%, as it is the second child. With the information given in the question though, we know both children already exist, and at least one is a girl. This of course removes the 25% probability option of Boy/Boy existing, and therefore we have the 3 options stated previously remaining, each at 33.33% as probabilities always have to add up to 100%.

Boy/Girl IS NOT the same as Girl/Boy. Cannot be, never ever will be. If you have 2 children, one is a 12 year old girl and the other a 9 year old boy, is that the same as having a 12 year old boy and a 9 year old girl?

Not reached 10 pages yet but Smee is now claiming both answers can be right, they can but not for the same question.

Who would have thought that the such a long thread would involve Glupton/Smee arguing with people?

What’s the odds of that?

Blimey so close to 10 pages all is quiet.

Scotland’s currently looking at methods of improving adult literacy and numeracy, as according to UNESCO 23% of Scots have trouble with these. It looks like this help may have come too late for some.

I’m not reading all that!!

How many chuffin’ posts??