talkmagic.co.uk

Oooops - double post

i think you're fooling yourself mate...

"A couple have two children (and they are a normal couple with a 50:50 chance of having a girl or a boy).
You are introduced to one of their children who is a girl. What is the probability that the other child is also a girl?"

unless you have missed out a part...then it is 50%...

IAIN wrote:i think you're fooling yourself mate...

Trust me - I'm not .

Re-read the question.

It is not a trick question.

You are introduced to a couple and you know that at least one of their children is a girl. What are the odds that the other is a girl?

I just knew that this was gonna happen ..........

...... and the answer is not 50/50 .....

i've googled the answer, but i still don't agree!! haha

it may be technically mathematically correct, but i believe otherwise...

EDIT: I'll leave this for someone else to have fun with.

Iain is right - technically mathematically correct, but only under certain circumstances and not really a real world or practical way to measure probability

100%?
As in the difference in the meaning; 'You are introduced to one of their children who is a girl' and, 'You are introduced toone of their children who is a girl.'
As in the difference between one of their two children, and one of their two girls?

EckoZero wrote:Iain is right - technically mathematically correct, but only under certain circumstances and not really a real world or practical way to measure probability

50/50 is not the correct answer .........


I'm off to bed now, but let me try and help you in the right direction .

If a couple have 2 children (and we know nothing of their sexes) - how many different pairings are possible ??

To re-phrase the puzzle slightly:

Suppose you and your friend were sat at a table and your friend flipped 2 coins and covered them both so that you didn't see any of them. He then looked at both of them and told you that at least one of these was a head (note, that he doesn't tell you which one).
What would be the odds that the other coin was a head ??
If you say 50/50, you're wrong.

How many different ways is it possible to throw 2 coins ??
You know that one of these is a head, so you can eliminate one pairing.

...... carry on .........

moonbeam wrote:

EckoZero wrote:Iain is right - technically mathematically correct, but only under certain circumstances and not really a real world or practical way to measure probability

50/50 is not the correct answer ..........

Nah I got the answer, posted it then edited it to keep it going for a while.
Iain got the answer too so I was commenting on that - that it's not a real world and practical way to measure probability and opens up a whole new can of worms...

Should be fun to see where this one ends up

I know what you are getting at but I still disagree with the maths.

Let me use this example to show why I don't agree:

I was working in a shop when I was 17 and a man came in to buy a lottery ticket. He asked for a lucky dip ticket (where the numbers are randomly generated) and when I gave him his ticket he commented that one of his numbers was the number 2.

"But that's unfair," he protested. "Two came up last week and I think you'll find it very unlikely that it will come up two weeks in a row!"

The man was confused in his use of statistics. It is true that the chances of the same number coming up two weeks in a row (i.e. next week and the week after) are low.

Assuming that the probability of that number appearing is 'y', then the probability of it appearing two weeks in a row is y squared.

However, once it has already come up one week, the probability of it coming up next week is still 'y', as the likelihood of the number being drawn each week is unaffected by the previous week's draw.

Assuming that the fact that they have had one girl does not biologically affect the liklihood of them having a girl again (which makes no sense) then the answer is 50/50

Have just reread the previous answers and realised that others have already said pretty much the same thing.

Having looked at the statistics every way, I still think that it must be 50/50

Ok, so Im reaching out on a limb here...

Suppose they told you the children are identical twins. The probability would be 100% the second child is female Likewise non-identical twins, the probability would be 0%

mathematically, the answer is 1/3...

but with maths applied to a physical thing, i believe we can technically prove we all have 1.4 legs or something weird...

every time you spawn a child, there is a base 50% chance of boy or girl...

we could open up this maths piece though, by introducing siamese twins, hemaphrodites and of course, jim davidson...

IAIN wrote:mathematically, the answer is 1/3...

but with maths applied to a physical thing, i believe we can technically prove we all have 1.4 legs or something weird...

You can use induction to "prove" that we all have 1 leg, or to "prove" that everyone in the country is actually female. But the maths doesn't quite stand up in these cases and wouldn't fly with a mathematician.

The 1/3 answer is technically correct but most people won't agree with you, in the same way that most people won't accept the answer to the Monty Hall problem. It seems like a pretty standard thing that people refuse to accept the maths on these kind of things because "it doesn't seem right to me", I know a couple of mathematicians that can prove the Monty Hall problem but still refuse to accept it!
As we all know, ignorance is bliss; and knowing why the answer is right can sometimes make your head hurt.

Edit: A proof.... (i said "proof")

A couple has 2 children, here are the possible outcomes of those 2 children:
Boy Boy
Boy Girl
Girl Boy
Girl Girl

Knowing one is a girl removes the boy boy option and rearranging them below illustrates the answer quite nicely I think:
Girl Boy
Girl Boy
Girl Girl

Now I sit back and wait for someone to argue that Boy Girl and Girl Boy are the same thing...

well, cos they are...

the riddle doesnt stipulate working out which sex came first (uh huh huh huh - i said....)

so whether it be boy/girl, or girl/boy...then no, it doesnt count...

please, no one read these posts in an "angry voice", its just sometimes applying maths to certain other things just doesnt work...

someone having a kid, is one of 'em...there's usually only two main choices each time...and it just depends on the fastest swimmer!

IAIN wrote:well, cos they are...

the riddle doesnt stipulate working out which sex came first

Fair enough, but in this case the Boy Girl option would be twice as likely as the Girl Girl option so you still get the same result.

Can we move on to a new riddle now? Preferably not maths related.