Or another way to view it is if I wanted to take, let's say I have some other random variable. I'm running out of letters here. Let's say I have the random variable A, and I define random variable A to be X minus Y. So what's its expected value going to be? The expected value of A is going to be equal to the expected value of X minus Y, which is equal to, you can either view it as the expected value of X plus the expected value of negative Y, or the expected value of X minus the expected value of Y, which is the same thing as the mean of X minus the mean of Y. So this is what the mean of our random variable A would be equal to. All of this is review, and I'm going to use this when we start talking about distributions that are sums and differences of other distributions.