Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: probability question
Replies: 9   Last Post: Mar 13, 2008 4:08 PM

 Messages: [ Previous | Next ]
 RGVickson@shaw.ca Posts: 1,677 Registered: 12/1/07
Re: probability question
Posted: Mar 12, 2008 12:00 AM

On Mar 11, 6:56 pm, Steven <sgottlie...@hotmail.com> wrote:
> Suppose you meet me on a street corner and I introduce you to my son who is with me. I inform you that I have another child at home. What is the probability that my other child is a girl.
> I looked at the sample space which I claim is bb, bg, gb and so the answer is 2/3. Is this correct?
> Steven

Yes, provided that you don't say which child is older. If you do say
which is older, the probability becomes 1/2! You can also look at the
problem this way: you toss a coin twice and announce that you got at
least one Head. What is the probability the other outcome was a Tail?
Again, the probability that the other outcome is a Tail is 2/3 if you
don't say whether your announced Head was first or second, and is 1/2
if you do announce its position.

R.G. Vickson

Date Subject Author
3/11/08 Steven
3/11/08 Dan Heyman
3/11/08 Bob Delaney
3/12/08 RGVickson@shaw.ca
3/13/08 The World Wide Wade
3/12/08 quasi
3/12/08 The World Wide Wade
3/12/08 quasi
3/12/08 quasi
3/12/08 briggs@encompasserve.org