A random sample of 49 cast aluminum pots is taken from a production line once every day.The number of defective pots is counted.The proportion of defective pots has been closely examined in the past and is believed to be 0.05.The sample proportions for the week are shown in the accompanying table. Is the production process in control?
A) No,because the sample proportions show a downward trend.
B) No,because the sample proportions fall within the upper and lower control limits.
C) Yes,because the sample proportions show a downward trend.
D) Yes,because the sample proportions fall within the upper and lower control limits.

Question

A random sample of 49 cast aluminum pots is taken from a production line once every day.The number of defective pots is counted.The proportion of defective pots has been closely examined in the past and is believed to be 0.05.The sample proportions for the week are shown in the accompanying table.  Is the production process in control?
A) No,because the sample proportions show a downward trend. 
B) No,because the sample proportions fall within the upper and lower control limits. 
C) Yes,because the sample proportions show a downward trend. 
D) Yes,because the sample proportions fall within the upper and lower control limits.

Quizplus · Accepted Answer

The question states that a sample of 49 pots is taken once every day, which suggests the use of a control chart. The proportion of defective pots is known to be 0.05, which can be used to calculate the control limits for the chart. The table shows that all the sample proportions fall within the control limits, which indicates that the process is in control. The fact that there is a slight downward trend in the sample proportions does not necessarily indicate that the process is out of control, as long as the samples remain within the control limits. Therefore, the correct answer is D.

A Random Sample of 49 Cast Aluminum Pots Is Taken