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 Measirement 17 15 15 17
Machine 2 Measurement 16 25 18 25
Machine 3 Measurement 23 24 23 22
What are the Mean chart three-sigma upper and lower control limits?
a) 22 and 18
b) 23.16 and 16.84
c) 22.29 and 16.71
d) 23.5 and 16.5
e) 24 and 16