J K 2s 2 B C D E F G H L M N 0 P Q R R S 1 Chapter 7 Pro 11 2 3 Given: An operation has a standard deviation of 1.5 minutes per piece. The goal is to estimate the mean time per piece to within 0.4 minutes of its true value with a confidence of 95.5%. 4 5 6 n = 7 8 where: 9 = = Number of normal standard deviations for desired confidence 10 s = Sample standard deviation 11 e = Maximum acceptable amount of time error 12 13 Number of Observations Needed: 14 15 Using: = 2.00: 16 17 zs 2 18 N e : 19 20 Using 2 = 2.01 21 22 zs 2 23 n = e 24 25 where: 26 = = Number of normal standard deviations for desired confidence (95.5%) 27 Using App. B Table A, we look for 955/2 = .4775: 4775 is midway between.4772 (= = 2.00) & .4778 = 2.01). 28 5 = Sample standard deviation (1.5 from above) 29 e =Maximum acceptable amount of time error (0.4 from above) 30 31 Conclusion: How many observations 32