Assume that items produced are supposed to be normally distributed with mean 35 and standard deviation 3. To monitor this process, subgroups of size 5 are sampled. If the following represents the averages of the first 20 subgroups, does it appear that the process was in control?
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Subgroup No.
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X
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Subgroup No.
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X
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1
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34.0
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6
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32.2
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2
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31.6
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7
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33.0
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3
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30.8
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8
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32.6
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4
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33.0
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9
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33.8
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5
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35.0
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10
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35.8
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Subgroup No.
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X
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Subgroup No.
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X
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11
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35.8
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16
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31.6
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12
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35.8
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17
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33.0
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13
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34.0
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18
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33.2
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14
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35.0
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19
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31.8
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15
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33.8
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20
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35.6
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