What I want to know is, what is the probability that I picked out a fair coin given that I got 4 out of 6 heads? So before moving on, let's do a little bit of a review of Bayes' theorem. And I think that'll give us a good framework for the rest of this problem. 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.