Motor oil is packaged and sold in plastic bottles. The bottles are often handled quite roughly in delivery to the stores (bottles are packed in boxes, which are stacked to conserve truck space), in the stores themselves, and by consumers. The bottles must be hardy enough to withstand this treatment without leaking. Before leaving the plant, the bottles undergo statistical process control procedures. Five out of every 10,000 bottles are sampled. The burst strength (the pressure required to burst the bottle) is measured in pounds per square inch (psi). The process is designed to produce bottles that can withstand as much as 800 psi. The burst strengths of the last 30 samples were recorded.
a. Draw the appropriate control chart(s).
b. Does it appear that the process went out of control? If so, when did this happen, and what are the likely causes and remedies?