# On

First off, the article I’m referring to is:
http://www.straightdope.com/classics/a3_189.html

I disagree with Jordan Drachman’s second scenario.

You only know that one of the two children is a girl. Case 1 and case 3 are therefore identical.

male-female
male-male
female-female.

We know that the second outcome is impossible, therefore there is a 1 in 2 chance that the other child is a boy,
and a 1 in 2 chance that the other child is a girl.

-Dan Papasian

You’re making a common mistake Dan. You mention three cases above, but your three cases do not have equal probability!

There are four possible outcomes:
oldest child = girl, youngest child = boy
oldest child = boy, youngest child = girl
oldest child = boy, youngest child = boy
oldest child = girl, youngest child = girl

So in your case, the male-female combination has probability = 1/2. The other choices have probability 1/4.

Pssst, Arnold, you think this thread should have a better title than “On”?

bugg, you used quotes in the title block, didn’t you?

I’m sure you’re right, Irishman, but the title as it is now has a zen-like simplicity that intrigued me. If our friend bugg asks for a less cryptic title I will be glad to oblige.

Here’s three previous threads that seem to be relevant

And here’s two that might be