Re: probability question
- From: The World Wide Wade <aderamey.addw@xxxxxxxxxxx>
- Date: Thu, 13 Mar 2008 13:08:53 -0700
In article
<b66d6af9-9850-477f-9e18-1892ebafdfd1@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Ray Vickson <RGVickson@xxxxxxx> wrote:
On Mar 11, 6:56 pm, Steven <sgottlie...@xxxxxxxxxxx> 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?
"Other" is not well-defined in this coin experiment, but it is in the
OP's problem. I think your coin example models the following: You meet
me on the corner, I tell you I have two kids at home, you ask if
they're both girls, and I say no. Then the probability is 2/3 that I
have a daughter. But if I'm out with one of my two kids, who's a boy,
then the probability my other kid is a girl is 1/2 - assuming I'm
equally likely to have my other kid with me. I think this is a better
model for the OP's problem. The coin problem analogous to this is: I
have two coins, I toss each, then randomly choose the result of one of
the tosses to announce. If I say heads, what is the probability the
other toss is tails?
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
- References:
- probability question
- From: Steven
- Re: probability question
- From: Ray Vickson
- probability question
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