So Bayes' theorem, and let me do it in this corner up here. Bayes' theorem tells us the probability of both A and B happening, that upside down U is just intersection in set theory, but it's essentially saying it's a set of events in which both A and B occur. That's equal to the probability of A occurring given B times the probability of B, which is also equal to the probability of B occurring given A times the probability of A. I think this should make some intuition for you. If it doesn't, it might be a good idea to watch the conditional probability videos. But what we can do is we can rearrange this equation right here. If we just divide both sides by the probability of B, we get the probability, and I'll do this in a vibrant color, the probability of A given B is equal to the probability of B given A times the probability of A divided by the probability of B. I just took this equation, divided both sides by the probability of B, and I got this. So what is A and B in the problem we're trying to figure out?