11 The time needed for performing a machining operation is to be investigated. Historically, the process has had a standard deviation equal to 0.182 minutes. The means (in minutes) of 39 samples of n = 6 are: 00:38:24 Mc Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 3.98 3.73 3.97 3.79 3.93 3.78 3.88 3.83 3.85 3.94 3.82 3.79 3.83 Sample Mean 14 3.81 3.77 3.74 3.77 3.78 3.80 3.83 3.96 3.86 3.98 3.80 3.82 3.80 15 16 17 18 19 20 21 22 23 24 25 26 Mean Control Limits b. Is the process in control? No O Yes Sample 27 28 29 The average of the 39 sample means is equal to 3.84. a. Construct an-chart for this process with two-sigma limits. (Round the final answers to 2 decimal places.) 30 31 32 33 34 35 36 37 38 UCL 39 Mean 3.77 3.80 3.84 3.90 3.89 3.97 3.79 3.94 3.96 3.88 3.74 3.83 3.80 LCL

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