9.78 Construct a 90% confidence interval for / in Exercise 9.43 on page 295. Were we justified in assum- when we constructed the confidence ing that interval for - 142? 9.43 A taxi company is trying to decide whether to purchase brand A or brand B tires for its fleet of taxis. To estimate the difference in the two brands, an exper- iment is conducted using 12 of each brand. The tires are run until they wear out. The results are Brand A: 136,300 kilometers, 81 5000 kilometers. Brand B: 238, 100 kilometers, 82 6100 kilometers. Compute a 95% confidence interval for HA - B as- suming the populations to be approximately normally distributed. You may not assume that the variances are equal.