7.8 Let x be the number of courses for which a randomly selected student at a certain university is registered.

The probability distribution of x appears in the following table:

x 1 2 3 4 5 6 7 p(x) .02 .03 .09 .25 .40 .16 .05

a. What is P(x 5 4)?

b. What is P(x # 4)?

c. What is the probability that the selected student is taking at most five courses?

d. What is the probability that the selected student is taking at least five courses? more than five courses?

e. Calculate P(3 # x # 6) and P(3 , x , 6). Explain in words why these two probabilities are different.