Well, apparently cross multiplication has not been taught yet. I now know this because when I asked DS if he knew what it was, I was met with a blank stare and "what's that?" LOL!

Of course, a lot of methods he's learning are new to me. The math curriculum is Everyday Math and there's something called the lattice method that I don't really get and DS doesn't really care for. <sigh> It doesn't take much to make me realize just how long ago it was that I was in school...

Thanks everyone.