The mean is the center of mass of the graph of the probability mass function (Figure 2.7). The center of mass is computed by multiplying the height of each line by its value on the horizontal axis, and then adding the products. The value are 0,1,2, and 3. The heights are P(X=0) = 0.48, P(X=1) = 0.39, P(X=2) = 0.12, and P(X=3) = 0.01. The mean is therefore