A soft drink filling machine is set up to fill bottles with 12 ounces of soft drink. The standard deviation s is known to be 0.4 ounces. The quality control department periodically selects samples of 16 bottles and measures their contents. Assume the distribution of filling volumes is normal

a. Determine the upper and lower control limits and explain what they indicate.
b. The means of six samples were 11.8, 12.2, 11.9, 11.9, 12.1, and 11.8 ounces. Construct an X bar chart and indicate whether or not the process is in control.

a. LCL = 11.7
UCL = 12.3
b. Process is in control