The manager of a fast-food restaurant wants to be sure that, on average, customers are served within 4 minutes from the time the order is placed. He is particularly concerned about the staff working during the early morning shift. From a random sample of 41 orders, the mean time was 3.75 minutes with a standard deviation of 1.2 minutes. (a) Is there convincing evidence at the a = 0.05 significance level that the true mean service time during the early morning shift is less than 4 minutes?