This can be used as a warm-up question for another fun problem (which a friend of mine was asked during a phone screen for a position at DE Shaw): What if inste

This can be used as a warm-up question for another fun problem (which a friend of mine was asked during a phone screen for a position at DE Shaw): What if instead of telling you that they have two children at least one of them a girl, someone told you that they have two children at least one of them named, say, Linda? The assumption is that there are no boys named Linda, that the likelihood for a girl to be named Linda is not affected by having an older brother or sister, etc. It's not a trick question, nor a sociological problem requiring any knowledge about names, it's a purely mathematical puzzle. And, as you may have guessed, the solution is not the same as in the previous case (with two children at least one of them girl).