50. For a Calculus I class, the nal exam score Y and the average of the four earlier tests X are bivariate normal with mean m1  73, standard deviation s1  12 and mean m2  70, standard deviation s2  15. The correlation is r  .71. Find a.

b.

c.

d. , that is, the probability that the nal exam score exceeds 90 given that the average of the four earlier tests is 80