A technician in a quick oil change shop had the following service times (in minutes) for 20 randomly selected cars: a) Determine the mean and range of each sample b) Determine the mean of the sample means (grand mean) and the ranges. c) Assuming a standard deviation of 0.086 and a z value of 3 , calculate the upper and lower control limits for the sample mean and range. Indicate if the process is in control and why or why not. d) Assume standard deviation is not known. Use the alternate method and calculate the upper and lower control limits for the sample mean and range. Indicate if the process is in control and why or why not