Computer upgrades have a nominal service time of 80 minutes. Regular samples of service times have been taken and the results are as listed.

  1. Computer upgrades have a nominal service time of 80 minutes. Regular samples of service times have been taken and the results are as listed.

a. Determine upper and lower control limits for mean and range charts. Is the process in control? Explain.

b. If the customers expect a service time of 80 minutes, with an upper limit of 81 minutes, what is the process capability and defective rate in terms of ppm (parts per million)? Is the process capable? Explain. Assume that the process is normally distributed.