A NAPA auto parts supplier wants information about how long carowners plan to keep their cars. a simple random sample of 31 carowners results in a mean of 7.01 years and a standard deviation of3.74 years, respectively. Assume the sample is drawn from anormally distributed population.
a) Find a 95%confidence interval estimate of the mean.
b) Find a 95% confidence interval estimate of the populationstandard deviation.
c) If several years pass and you want to conduct a new survey toestimate the mean length of time that car owners plan to keep theircars, how many randomly selected cars owners must you survey?Assume you want 99% confidence that the sample mean is within 0.25year of the population mean,also assume the standard deviation is3.74 years.
