So this is a 1 1 4th probability. And that makes sense. If we've got doubles, and one of them's a four-sided die, we either have doubles at one, doubles at two, doubles at three, or doubles at four. You see that here, doubles one, doubles two, doubles three, doubles four. Well, given that, what's the probability that the four-sided die is a four? Well, that means that's one of these four outcomes where it's a double fours right over here. All right, what is the probability of A and B?