A sample of 40 different payroll departments found that employees worked an average of 240.6 days a year. If the population standard deviation is 20 days, find the 95% confidence interval for the...

 A sample of 40 different payroll departments found that employees worked an average of 240.6 days a year.  If the population standard deviation is 20 days, find the 95% confidence interval for the average number of days μ worked by all employees who are paid through payroll departments.