Question

2.73 Surface roughness of pipe. Refer to the Anti-corrosion Methods and Materials (Vol. 50, 2003) study of the sur- face roughness of coated oil field pipes, Exercise 2.20 (p. 37). The data (in micrometers) are repeated in the table. Give an interval that will likely contain about 95% of all coated pipe roughness measurements. ROUGHPIPE - - - 1.72 2.50 2.16 2.57 2.64 1.26 2.13 1.06 2.24 2.31 2.03 1.09 1.40 2.05 1.19 2.13 1.27 1.51 2.41 1.95 - - - - - - - - Source: Farshad, F., and Pesacreta, T., “Coated pipe interior surface roughness as measured by three scanning probe instruments.” Anti-corrosion Methods and Materials, Vol. 50, No. 1, 2003 (Table III). - - - - - ------------------- - -- - --------

Answer 1

Let denotes the sample mean, s denotes the sample standard deviation and n denotes the sample size. Here, 1.881, s20.2745, s 0.5239,. 20 The margin of error is: 0.524 0.524 S МЕ- *to.025,19 V20 2.093024 0.245000 = 0.245 *t 1-0.950 _ ,19 2 V20 a 95 percent confidence interval population mean u is *t 1-0.950 ,19 2 0.524 - 1.881 ± V20 to.025,19 0.524 1.881 2.093024 20 - 1.881 ± 0.245000 = (1.636000, 2.126000) (1.64, 2.13) 23