8.13 The downtime per day for a certain computing facility averages 4.0 hours, with a standard deviation of 0.8 hour.

P Aaq i=1Xi 7 aB = P(nX 7

a) = P(X 7 a>n)

a Find the probability that the average daily downtime for a period of 30 days is between 1 and 5 hours.

b Find the probability that the total downtime for the 30 days is less than 115 hours.

c What assumptions are necessary for the answers in parts

(a) and

(b) to be valid approximations?