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? We want to try to figure out the probability that I picked out a fair coin given that I got 4 out of 6 heads. So in this situation, A is that I got a fair coin. A is equal to picked fair coin.