The file P08_06.xlsx contains data on repetitive task times for each of two workers. John has been doing this task for months, whereas Fred has just started. Each time listed is the time (in seconds) to perform a routine task on an assembly line. The times shown are in chronological order.

Calculate a 95% confidence interval for the mean time it takes John to perform the task. Do the same for Fred. Round your answers to one decimal place, if necessary.

	John	Fred
Lower limit
Upper limit

Do you believe both of the confidence intervals in part a are valid and/or useful? Why or why not?

SelectJohnFredItem 5 's confidence interval is to the left of SelectJohnFredItem 6 's, indicating that SelectJohnFredItem 7 's times tend to be lower. However, a look at the time series plot of their times would show that SelectJohnFredItem 8 has been improving, whereas SelectJohnFredItem 9 has stayed (approximately) constant.

Which of the two workers would you rather have, assuming that task time is the only issue?

1. SelectJohnFred