Here's the question "In a faraway land long ago, boys were valued more than girls. So couples kept having babies until they had a boy. The frequency of boys and girls in the populations as a whole remained equal, but what was the expected frequency of girls per family? (Assume that each sex is equally likely)" I have a hint (see attachment) I kind of see what they want, but I don't really know how to get it. I tried to find the expected value for a given case (let's say they have n babies), but it doesn't really come out to what they have. I don't really know how the fact that the frequency of boys and girls remains equal fits into the problem, either. Any help is appreciated.