The shape of the distribution of the time required to get an oil change at a 20-minute oil-change facility is unknown.However, records indicate that the mean time is 21.2 minutes , and the standard deviation is 4.8minutes.

(a) To compute probabilities regarding the sample mean using the normalmodel, what size sample would berequired?

(b) What is the probability that a random sample of n=45 oil changes results in a sample mean time less than 20 minutes?