In Design and Analysis of Experiments, 9th edition (Wiley, 2017), D. C. Montgomery described an experiment in which the tensile strength of a synthetic fiber was of interest to the manufacturer. It is suspected that strength is related to the percentage of cotton in the fiber. Five levels of cotton percentage were used and five replicates were run in random order, resulting in the following data. Cotton Percentage Tensile Strength 15 7 7 15 11 9 20 12 17 12 18 18 25 14 18 18 19 19 30 19 25 22 19 23 35 7 10 11 15 11 Does cotton percentage affect breaking strength? Draw comparative box plots and perform an analysis of variance. Use = 0.05.

Plot average tensile strength against cotton percentage and interpret the results. Analyze the residuals and comment on model adequacy.