Marketing and Consumer Behavior According to a recent survey, Americans are keeping their cars longer.21 Some of the reasons may include the poor economy and better-built vehicles. A random sample of new- and used-car owners was asked how long they usually kept their car (in months).
a. Find a 99% confidence interval for the true mean time people keep a new car.
b. Find a 99% confidence interval for the true mean time people keep a used car.
c. Using your answers in parts (a) and (b), do you think new-car owners and used-car owners keep their cars for different lengths of times? Justify your answer.