Checkout time at a supermarket is monitored using a mean and a range chart. Six samples of n = 20 observations have been obtained and the sample means and ranges computed: Sample Mean Range Sample Mean Range 1 3.06 .42 4 3.13 .46 2 3.15 .44 5 3.06 .46 3 3.11 .41 6 3.09 .45 Factors for three-sigma control limits for formula157.mml and R charts FACTORS FOR R CHARTS Number of Observations in Subgroup, n Factor for formula158.mml Chart, A2 Lower Control Limit, D3 Upper Control Limit, D4 2 1.88 0 3.27 3 1.02 0 2.57 4 0.73 0 2.28 5 0.58 0 2.11 6 0.48 0 2.00 7 0.42 0.08 1.92 8 0.37 0.14 1.86 9 0.34 0.18 1.82 10 0.31 0.22 1.78 11 0.29 0.26 1.74 12 0.27 0.28 1.72 13 0.25 0.31 1.69 14 0.24 0.33 1.67 15 0.22 0.35 1.65 16 0.21 0.36 1.64 17 0.20 0.38 1.62 18 0.19 0.39 1.61 19 0.19 0.40 1.60 20 0.18 0.41 1.59 a. Using the factors in the above table, determine upper and lower limits for mean and range charts. (Round your intermediate calculations and final answers to 4 decimal places.) Upper limit for mean Lower limit for mean Upper limit for range Lower limit for range b. Is the process in control? Yes No