1.

A Quality Analyst wants to construct a control chart for determining whether three machines, all producing the same product, are under control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results : Machine #1 measurements [15, 15, 18, 13]; Machine #2 measurements [ 23, 18, 14, 18]; Machine #3 measurements [ 16, 18, 12, 17]. Using the factors for three sigma control limits, what are x-bar chart upper and lower control limits?

a.

18.22and 14.62

b.

21.28and 11.55

c.

36.42and -3.583

d.

23.22and 9.617