The Long Last Tire Company, as part of its inspection process, tests its tires for tread wear under simulated road conditions. Twenty samples of three tires each were selected from different shifts over the last month of operation. The tread wear is reported below in hundredths of an inch.

Sample Tread WearSampleTread Wear 144 41 191111 33 34 239 31 211251 34 39 338 16 251330 16 30 420 33 261422 21 35 534 33 361511 28 38 628 23 391649 25 36 7 40 15 341720 31 33 8 36 36 341826 18 36 9 32 29 301926 47 26 1029 38 342034 29 32

(a) Find the center line, sample standard deviation, and action limits for this sampling scheme. (b) Draw a quality control chart for this process and from your chart comment if the process is in control.