21. Central Airlines would like to set up a control chart to monitor its on-time arrival performance. Each day over a 10-day period Central Airlines chose 30 flights at random and tracked the number of late arrivals in each sample.

The results are as follows:

a. (*) Calculate .

b. (**) Set up a p chart to track the proportion of late arrivals. (Note: Each sample consists of 30 observations.)

c. (***) Airline travel is characterized by busy and slow seasons. As a result, what is “normal” during one time of the year wouldn’t be “normal” at some other time.What difficulties might arise as a result of using a single control chart to track the proportion of late arrivals? What could Central Airlines do about this?

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DAY SAMPLE SIZE NO. OF LATE- ARRIVING FLIGHTS 1 30 2 30 2 3 3 30 4 45 30 0 30 1 6 30 6 30 4 10 7880 30 9 30 30 235 5