The performance ratings of two sports cars, the Mazda RX7 and the Nissan 300ZX, are to be compared. A random sample of 40 drivers is selected to drive the two models. Each driver tries one car of each model, and the 40 cars of each model are chosen randomly. The time of each test drive is recorded for each driver and model. The difference in time (Mazda time Nissan time) is computed, and from these differences a sample mean and a sample standard deviation are obtained. The results are 5.0 seconds and sD 2.3 seconds. Based on these data, which model has higher performance? Explain. Also give a 95% confidence interval for the average time difference, in seconds, for the two models over the course driven.