8. A manufacturer is attempting to estimate the mean number of miles that its new XJB- 60 automobile tires will last before wearing out. A sample of 49 tires are selected and ran on a test vehicle. The mean mileage for the sample was 63,500 miles with a standard deviation of $21,000 miles. Construct a 95% confidence interval for the mean miles that the tires will last. 9. Suppose the same facts as in problem 8 above except that a sample size of 81 tires is selected. Would a confidence interval constructed with this new sample size be wider or narrower than the confidence interval constructed in problem 8 ? Construct a 95% confidence interval with the same facts as problem 8 except for the new sample size. 10. Assume the same facts as in problem 8 except that a 99% confidence interval will be conducted. Construct the confidence interval, Is this confidence interval wider or narrower that the one conducted in problem 8 ? 11. A research survey is conducted to estimate the mean amount that individuals in a California town spend on gasoline per week. A sample of 64 individuals were selected and the mean amount that the people spent on gas was $43 with a standard deviation of $7. Construct a 90% confidence interval for the mean amount that all citizens of the town spend