7.17 Table 7.2 shows the joint distribution of fatalities and number of seat belts used by children under age 5. What is the “average” behaviour of X1 and X2, and how are they associated? Follow the steps below to answer this question.

a Find E(X1), V(X1), E(X2), and V(X2).

b Find Cov(X1, X2). What does this result tell you?

c Find the correlation coefficient between X1 and X2. How would you interpret this result?