So this variable, this random variable y, the probability that it's equal to one, you could view that as a success, is equal to p. The probability that it's a failure, that y is equal to zero, is one minus p. So you could view y, the outcome of y is really the, or whether y is one or zero is really whether we had a success or not in each of these trials. So if you add up n y's, then you are going to get x. And we use that information to figure out what the expected value of x is going to be. Because the expected value of y is pretty straightforward to directly compute. Expected value of y is just probability-weighted outcomes. So it's p times one plus one minus p, one minus p, times zero, times zero. This whole term's gonna be zero.