Hi! You mean like this?

Just delete the part you don't want, or put what you want between "[QUOTE] and [QUOTE]"
As to the two children question, forget it!
He answered the wrong question.
The way it was asked there is only one answer to it, and KV got it right.

Cheers.

Yes . Thanks lomaca

The fact of what they have or don't already have, is irrelevant to the answer.

If I flip a coin and I already have one heads, I still have a 50% chance of tails next spin.

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What is the difference between Girl-boy and Boy-Girl, they are the same thing.

Boy-boy is an invalid combination given the question.

There are two possible combinations

Girl Girl

Girl Boy

That's it.

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Of course a mathmatician, because he wouldn't want to create confusion, would ask the question thusly: "If at least one of the children is a girl" and then might get an answer other than 100% or 50%. But Woof's point is valid in that we have to get used to using half ar sed information if we want to win at handicapping (my phrasing not his).

KV

This problem is a classic case of conditional probability. The average person has trouble understanding it. The boy/girl problem can be tested by repeatedly tossing 2 coins and recording the results(say 20 times). There are 3 possible outcomes ( 4 really) - HH,HT,TT.
Now we ask what is the probability of the other coin being a TAIL given that one of them is a HEAD? Straight away we can ignore all the TT's from our sample (cross them off the list) because the question asks "given that one of them is a head". That will leave only HH's and HT's in the list. Now put a circle around any T in the list. You should find about a 2:1 ratio or a 2/3 to 1/3 Tails to Heads.

This better illustrates conditional probability. With the coin or the boy/girl examples there are 4 possible outcomes - HH, HT, TH, TT each with a 25% chance of occuring. When we ask the question "given that one of them is a ..." we are effictively saying that one of these situations did not happen. In the above example we eliminated TT leaving HT, TH, HH. Now we are left with 2 T's and 1 H with the corresponding H which we were told existed. So the probability of the other coin being a T is 2/3 and an H is 1/3.

Well we have convincing arguments supporting 50%, 66% and 100% depending on how you read the question, what I would be interested to see now is the rationalle behind the other options offered. Nanook? La Mer? I particularly liked Kenchar's explanation. It surprised me at first but then made me realise that a standard view of statistics is absolutely not essential to being a successful punter.

KV

In my case it was by multiplying 0.5 by 0.5 which gives a result of 0.25, which would be correct other than for the issue of the prior knowledge of knowing that one of the children has already been identified as a girl.

i would like to hear jfc's thoughts on this becouse as it stands i'm wity cp...
...................cheers....slowman.............. ....

I didn't really read the question and multiplyed 0.5x0.5x0.5.......don't really know why.......don't really care, but one thing I do know is that 98% of the population who suffer from heart disease own a colour television?

nanook