Amertron produces electrical wiring in 100-foot rolls. The quality inspection process involves selecting rolls of wire at random and counting the number of defects on each roll. The last 20 rolls examined revealed the following numbers of defects:

Roll Number of Defects Roll Number of Defects 1 4 11 2 2 6 12 5 3 2 13 5 4 4 14 7 5 1 15 4 6 9 16 8 7 5 17 6 8 5 18 4 9 3 19 6 10 3 20 4

a. If the number of defects per 100-foot roll of wire follows a Poisson distribution, what is the estimate of c obtained from these observations?

b. Using a normal approximation to the Poisson, what are the three-sigma control limits that you would use to monitor this process?

c. Are all 20 observations within the control limits?