The Occupational Safety and Health Administration (OSHA) mandates certain regulations that have to be adopted by corporations. Prior to the implementation of the OSHA program, a company found that for a sample of 40 randomly selected months, the mean employee time lost due to job-related accident was 45 h. After implementation of the OSHA program, for a random sample of 45 months, the mean employee time lost due to job-related accidents was 39 h. It can be assumed that the variability of time lost due to accidents is about the same before and after implementation of the OSHA program (with a standard deviation being 3.5 h):
a. Find a 90% confidence interval for the difference in the mean time lost due to accidents.
b. Test the hypothesis that implementation of OSHA program has reduced the mean employee lost time. Use a level of significance of 0.10.