A small ferry runs every half hour from one side of a large river to the other. The num- ber of cars X on a randomly chosen ferry trip has the probability distribution shown below. You can check that mX = 3.87 and sX = 1.29.
Cars: 0 1 2 3 4 5
Probability: 0.02 0.05 0.08 0.16 0.27 0.42

Find and interpret the mean.