Dr Herbie said:
It's 50%.

The sex of the second child is not affected at all by the sex of the first child; knowing that one of the children is a girl is irrelevant in detemining the sex of the other.

Trust me, I'm a Doctor (of biology) Big Smile

Herbie
Dr Herbie said:
...The sex of the second child is not affected at all by the sex of the first child...


Well, unless they are monozygotic twins, then the sex of the second is determined by the sex of the first and the probability of the second being a girl is, for all practical purposes, 100% Smiley