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 sample proportions fall within the upper and lower control limits, indicating that the production process is in control. A downward trend in the sample proportions would only be a cause for concern if the proportions were falling outside of the control limits.

A Random Sample of 49 Cast Aluminum Pots Is Taken