One of the stages in the process of making denim cloth at the Southern Mills Company is to spin cotton yarn onto spindles for subsequent use in the weaving process. Occasionally the yarn breaks during the spinning process, and an operator ties it back together. Some number of breaks is considered normal; however, too many breaks might mean that the yarn is of poor quality. In order to monitor this process, the quality-control manager randomly selects a spinning machine each hour and checks the number of breaks during a 15-minute period. Following is a summary of the observations for the past 20 hours: Sample Number of Breaks Sample Number of Breaks

1 8 11 1
2 10 12 6
3 9 13 1
4 8 14 0
5 6 15 4
6 10 16 8
7 4 17 4
8 10 18 5
9 9 19 0
10 8 20 7

Required:
a. What is the average number of yarn breaks for this data?
b. Construct a c -chart using 3Q limits for this process and indicate if the process was out of control at any time.