"For a given couple with two children, if one is female what is the probability that the other child will also be female?" This question was asked to me in a recent interview. The interviewer and I disagreed on the answer. What is yours?

"For a given couple with two children, if one is female what is the probability that the other child will also be female?" This question was asked to me in a recent interview. The interviewer and I disagreed on the answer. What is yours?