At a junk yard a study was conducted using 48 cars and found that the average mileage on a car before it was junked was 164,000 and the population standard deviation is known to be approximately 28,000. construct a 99% confidence interval of what the actual average mileage is for a car before it is junked.

According to a study conducted in 2015, 18% of shoppers said that they prefer to buy generic instead of name-brand products. suppose that in a recent sample of 1500 shoppers, 315 stated that they prefer to buy generic instead of name-brand products. at a 5% significance level, can you conclude that the proportion of all shoppers who currently prefer to buy generic instead of name-brand products is higher than .18? use both the p-value and the critical-value approaches.