Estimating Length of Car Ownership A NAPA Auto Parts supplier wants information about how long car owners plan to keep their cars. A simple random sample of 25 car owners results in 5 7.01 years and s 5 3.74 years, respectively (based on data from a Roper poll). Assume that the sample is drawn from a normally distributed population.

a. Find a 95% confidence interval estimate of the population mean.

b. Find a 95% confidence interval estimate of the population standard deviation.

c. If several years pass and you want to conduct a new survey to estimate the mean length of time that car owners plan to keep their cars, how many randomly selected car owners must you survey? Assume that you want 99% confidence that the sample mean is within 0.25 year (or 3 months) of the population mean, and also assume that s 5 3.74 years (based on the latest result).

d. When conducting the survey described in part (c), you find that the survey process can be simplified with a substantially reduced cost if you use an available database consisting of people who purchased a General Motors car within the past 10 years.
Would good results be obtained from this population?