The Journal of Testing and Evaluation (July 1992) published an investigation of the mean compression strength of corrugated fiberboard shipping containers. Comparisons were made for boxes of five different sizes: A, B, C, D, and E. Twenty identical boxes of each size were tested and the peak compression strength (pounds) recorded for each box. The accompanying figure shows the sample means for the five box types as well as the variation around each sample mean.

a. Explain why the data are collected as a completely randomized design.

b. Refer to box types B and D. Based on the graph, does it appear that the mean compression strengths of these two box types are significantly different? Explain.

c. Based on the graph, does it appear that the mean compression strengths of all five box types are significantly different? Explain.

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1,000 900 800 700 600 500 400 300 200 100 A В C D E Воx type Compression strength (Ib)