4. You test 12 VW trucks and 10 Toyota trucks for gas mileage. The sample of VT trucks had a mean of 16 km/liter with a standard deviation of 1 km/liter. The sample of Toyota trucks had a mean of 11 km/liter with a standard deviation of 0.8 km/liter. What is the 90% confidence interval for the true mean difference in gas mileage between these two truck types? Assume the gas mileages are normally distributed with equal variances.
5. What is section 9.9 in the book about?
? ? a. Confidence interval for a single mean