As expected the process average appears to have dropped a little below target (it was a little above before the change) and the standard deviation has reduced. It appears that the improvements have succeeded in reducing process variability.

a. Construct X̅ and R charts to determine if the process is in a state of statistical control.

b. What is your estimate of the average tread wear and the standard deviation of tread wear for this product?

c. What is your estimate of the average tread wear and the standard deviation of tread wear for this product?

Tread Wear Tread Wear Sample /100th inch) ch Sample (100th inch) 41 4038 13 24 28 15 25 18 2214 20 424 35 241915 31 2032 20 222516 34 2338 41 31 32 17 34 3425 29 39 36 18 26 20 23 29 27 32 19 26 36 45 22 35 38 20 36 2223 28 27 32 2 26 17 34 10 34 27 36 22 27 17 32 25 47 41 23 26 32 23 12 23 30 22 24 26 28 27 X and R