This right over here is the Greek letter mu, which is often used to denote the mean, so this is the mean of the random variable X. But how do we actually compute it? To compute this, we essentially just take the weighted sum of the various outcomes, and we weight them by the probabilities. So for example, this is going to be, the first outcome here is zero, and we'll weight it by its probability of 0.1. So it's zero times 0.1, plus the next outcome is one, and it would be weighted by its probability of 0.15, so plus one times 0.15, plus the next outcome is two, it has a probability of 0.4, plus two times 0.4, plus the outcome three has a probability of 0.25, plus three times 0.25, and then last but not least, we have the outcome four workouts in a week that has a probability of 0.1, plus four times 0.1. Well, we can simplify this a little bit. Zero times anything is just a zero, so one times 0.15 is 0.15, two times 0.4 is 0.8, three times 0.25 is 0.75, and then four times 0.1 is 0.4.