In article ,
(H Schinske) wrote:

wrote:

Well, in the first place, there is usually not a connection between the
gender of your first child and the gender of your second.

I think it's interesting, though, that before you have any children at all,
and
assuming you will at some point have two and only two, the odds of having
children of different sexes are only one in three (about a third of folks
with
two children have two boys, about a third have two girls, about a third have
one of each). Whereas if you've already had one baby, of either sex, your
chance of having one of each after your next birth magically goes up to one
in
two :-)

(Yes, I know why this happens. I just think it's cute. Humor me.)

--Helen

Um. I'd like to humor you, but I like probability more. And your
statement doesn't make any sense.

The probability that a hypothetical couple (HC) who will have 2 kids
will have one of each is one in two.
The HC's children will either come out as: BB, BG, GB, GG. 4
possibilities, each equally likely, 2 of the 4 possibilities give you
one of each, 2/4 = 50% = 1/2.

Once they've already had one baby, then the probability of having one of
each after the next birth is still 1/2.

Maybe you're thinking of the old puzzle which goes like this - I have
two children, at least one of whom is a boy. What's the probability that
the other is a boy?

The probability of my having two boys would be 1/3, because you've
narrowed it down to either: BB, BG, or GB.

(Note: To some extent, this depends on how you interpret the puzzle. For
lots more discussion, see for example:
http://www.curiouser.co.uk/us/kids.htm
http://www.icdc.com/~samba/marlright/children.htm
)

- Lynn