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Calculating Upper and Lower Control Limits

A particular magazine typically has 65% subscription renewals. A new advertising campaign is introduced to see if this can be increased. To monitor renewals, a sample of 300 subscribers is taken each month to see what percentage renew their subscription. What are the upper and lower control limits for a control chart for the proportion of renewals? If there are 210 out of 300 renewals in a monthly sample, does this indicate that an increase in the overall renewal rate has occurred?

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This solution provides answers in Excel for questions regarding upper and lower control limits.