6.1 (a) Explain the principles of Shewhart control charts for sample mean and sample range. (b) State the Central Limit Theorem and explain its importance in SPC. 6.2 The following are measures of the impurity. iron. in a fine chemical which is to be used in pharmaceutical products. The data is given in parts per million (ppm). Sample X1 X2 1 X3 15 X4 11 X5 8 2 15 14 16 6 3 11 14 13 7 6 9 4 5 15 15 10 9 5 9 15 7 12 9 6 8 11 8 14 7 11 13 12 5 12 9 8 6 10 15 10 9 12 8 4 6 12 14 10 9 10 10 10 9 11 14 13 14 16 12 12 7 15 10 18 9 13 11 11 7 16 16 14 11 7 14 15 10 10 13 7 9 16 12 17 13 10 17 17 11 9 4 8 14 5 18 8 11 9 11 6 19 9 13 9 10 7 20 10 15 10 13 10 12 16 iron content. Set up mean and range charts and comment on the possibility of using them for future control of the