A Manufacturer of Windows Produces One Type That Has a Plastic

Multiple Choice

A manufacturer of windows produces one type that has a plastic coating.The specification limits for the plastic coating are 30 and 70.From time to time the plastic coating can become uneven.Therefore,in order to keep the coating as even as possible,thickness measurements are periodically taken at four different locations on the window.15 subgroups were observed and each subgroup consists of the four thickness measurements taken across the windows at a particular time with the following results: mean of the means = = 50.05 and the average range of 8.85. Calculate the control limits for the X-bar chart.

A) (41.2 58.9)
B) (48.1 52.0)
C) (43.6 56.5)
D) (29.9 70.2)