The time needed for performing a machining operation is to be investigated. Historically, the process has had a standard deviation equal to 0.163 minutes. The means (in minutes) of 39 samples of n = 6 are: Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 3.73 3.87 3.77 3.93 3.77 3.79 3.90 3.94 3.82 3.80 3.79 3.68 3.70 Sample 14 15 16 17 18 19 20 21 22 23 24 25 26 Mean 3.72 3.69 3.90 3.90 3.85 3.70 3.79 3.83 3.96 3.77 3.69 3.82 3.80 Sample 27 28 29 30 31 32 33 34 35 36 37 38 39 Mean 3.78 3.84 3.76 3.86 3.72 3.94 3.66 3.93 3.94 3.82 3.96 3.78 3.68