The time needed for performing a machining operation is to be investigated. Historically, the process has had a standard deviation equal to .146 minute. The means (in minutes) of 39 samples of n = 6 are:

Construct an x-chart for this process with Two Sigma limits. Is the process in control?

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Sample Sample Mean 14. .3.81 15 . 3.83 l6. 3.86 17.-3.82 183.86 Mean Sample Mean 27 ...3.81 283.86 29.. 3.98 303.96 31 ....3.88 32.3.76 3 ..3.83 4..3.81 6 . .3.83 7 . 3.87 8 ...3.80 3.84 10 . . 3.80 3.88 20..3.87 21 3.84 35..3.86 30 ...3.80 3.84 38 .. . 3.79 30...3.85 23..3.89 3.86 133.88 26.3.90