On A Similar Theme - Probability Again

[Cloverjo]

I remember reading about a problem which went something like this:
Mr Smith has a daughter named Tallulah. What is the probability of his other child being a girl?

The answer was very surprising and counter-intuitive and not the same as the answer in Factor-Fiction's related thread, but the author went through every step and it all made sense. Unfortunately, I can't find the book or remember its title. Does anyone recognise this, and tell me the title or author?

[Old_Geezer]

Since that is obvious it hardly seems a worthwhile use of my time. Yuo may refer them to my posts on the other thread :-)

But no, I've not heard of a puzzle regarding a daughter named Tallulah. I'd be interested to see it if you ever find it.

[DTCwordfan]

I think some practice (live testing) is in order - any female volunteers?

[Old_Geezer]

Did you mean to post in the serious question thread ?

[DTCwordfan]

Yes, some light relief always helps the study of statistics, OG.....it helps us better memorise things.....

[PaulHDear]

I don't know the book, but the argument goes something like this.
Mr. Smith has two children (since he has a daughter and "another child"). A priori, he could have:
Girl+Girl
Girl+Boy
Boy+Girl
Boy+Boy
Each of these has a probability of 1/2 x 1/2 = 1/4 (25%). But the middle two (Boy+Girl and Girl+Boy) are the same, so we have:

2 girls = 25%
1 of each = 50%
2 boys = 25%

We know that the "2 boys" option is ruled out, because he has a daughter called Tallulah. So, were are left with "1 of each" or "2 girls". The probability of "1 of each" is twice as high as "2 girls". So, *given* that he has a daughter called Tallulah, there's only a 1/3 chance (33.3%) that his other child is a girl.

[mibn2cweus]

So what you're sayin' in effect is that, if we both flip coins and I peek at mine to see whether I have heads or tails, I then have a 50% better chance of winning by declaring, 'Odds!'

[Cloverjo]

Paul, that argument works when we don't know the name of the girl. There is a thread on that subject elsewhere on AB. The point is that knowing the unusual name of one of the children changes the probability of the other child being a girl to 1/2. See the link I posted at 3.40 on Thursday 30th Nov.

Incidentally, for others interested, I remember where I read the argument for the first time. It was a book called The Drunkard's Walk, and the girl in the problem is called Florida (as in my other link) not Tallulah. (My memory!)

The author explains it in a simpler way. You can see here by going to page 112 of Amazon's Look Inside function. (Hopefully)
http://www.amazon.com/The-Drunkards-Walk-Randomness-Rules/dp/0307275175

[fudgefudge]

hello