A cake manufacturing business based in London has 120 branches spread all over the city. All cakes are customized as per the needs of the customers, including type of cake and choice of toppings. For quality control and consistency, cakes are manufactured at a central location and distributed to the branches. Cakes are randomly inspected for errors such as the writing on the cake, toppings, delivery location, and type of cake. Even a single error makes a cake defective. The following data were collected over the last 30 days to see how many cakes turned out defective. Each sample has 200 randomly selected cakes.

a. What are the upper and lower control limits of a p-chart for the number of defective cakes? Use z = 3.
b. Is the process in statistical control?

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Sample 1 2 3 4 LO 5 6 7 8 9 10 11 12 13 14 15 Defects 20 14 8 14 15 11 13 18 14 12 9 17 13 15 14 Sample 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Defects 20 12 11 15 15 20 8 9 11 11 14 8 10 11 9