These data indicate the prices of 155 used BMW cars. Some have four-wheel drive (the model identified by the Xi type) and others two-wheel drive (the model denoted simply by the letter i).
(a) If we treat the data as samples of the typical selling prices of these models, what do you conclude? Do four-wheel drive models command a higher price as used cars, or are differences in average price between these samples typical of sampling variation?
(b) These cars were not randomized to the two groups. We also know that newer cars sell for more than older cars. Has this effect distorted through confounding the confidence interval in part (a)?