And how many of them involve event B being true? Well, the only one of these four that involve event B being true is this one right over here where we've got our doubles. So there is a 1 1 4th probability that if we assume, given that we've gotten doubles, the probability that the four-sided die is a four. 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.