Question 4 Your company manufactures plastic wrap for food storage. The tear resistance of the wrap, denoted by X, must be controlled so that the wrap can be torn off the roll without too much effort, but it does not tear too easily when in use. In a series of test runs, 15 rolls of wrap are made under carefully controlled conditions and the tear resistance of each roll is measured. The results of the test runs are as follows: Roll 1 2 3 4 X 5 6 78910 11 12 13 14 15 134 131 129 133 135 131 134 130 131 136 129 130 133 130 133 a) Calculate the sample mean (✗) and sample standard deviation (Sx) for this test series. b) Plot X vs. the Roll Number for this test series, and draw the horizontal lines corresponding to X, X - Sx, X + Sx, X - 2sx, and X + 2sx. The test results are used as the basis of a quality assurance specification. If X for a subsequently produced roll falls more than two standard deviations away from the test period average, the process is declared out of specification and production is suspended for routine maintenance. c) The following tear resistance values were obtained for rolls produced in 14 consecutive production runs subsequent to the test series: 128, 131, 133, 130, 133, 129, 133, 135, 137, 133, 137, 136, 137, 139. On the same lines obtained for the test series show the points corresponding to the 14 production runs (using a different symbol). Which measurements led to suspension of production? If you so choose, you can use a spreadsheet to perform your calculations and generate the plot.