And so the probability that he's picked a blue item, well that's one out of the two equally likely ones. So there is a one-half probability that he picks a blue garment given that he's picked a shirt. And that's because there's one blue shirt and one green shirt. Now let's look at the probability of B given A. Probability of B given A. So assuming that we've picked a blue garment, so assuming we've picked a blue garment, so it's either that one, that one, or that one, what's the probability that we have also chosen a shirt? Well, there's one, two, three possibilities, equally likely possibilities where we have a blue garment, and only one of those involves a shirt. So probability of B given A is one-third.