Last year you received an average of 129.2 complaints (i.e., individual items to be fixed under warranty) per new car sold, with a standard deviation of 42.1 complaints based on 3,834 new cars sold. This year you have set up a quality assurance program to fix some of these problems before the car is delivered. So far this year, you have had an average of just 93.4 complaints per new car sold with a standard deviation of 37.7, based on 74 cars sold so far.
a. To see if your new quality assurance program is working, what hypothesis testing method would you use?
b. Identify the populations, samples, and hypotheses.
c. Perform a two-sided test at the 5% level and report the results.