What they did there made no sense. There's no difference between Boy-Girl and Girl-Boy, because the order of birth has nothing to do with the question. The 13/27 thing suffers from the same problem. They say that BTu-BTu can only be counted once, and can't be counted again when you switch them around ... but at the same time, they're counting things twice by switching them around all the way through (saying, for example, that BTu-BWe is a different probability from BWe-BTu). Essentially, they're saying that the order doesn't matter when both boys are born on a Tuesday, but the order matters in every other case. They're not even applying their own logic evenly throughout the problem, it seems.

Even if, for some reason, you really want to use the irrelevent Tuesday information in the Math, it should still come out to 7/14.

Like ... are we missing something? Or is that just a surprisingly faulty math article?