Concrete specimens with varying height-to-diameter ratios cut from various positions on the original cylinder were obtained both from a normal-strength concrete mix and from a high-strength mix. The peak stress (MPa) was determined for each mix, resulting in the following data (“Effect of Length on Compressive Strain Softening of Concrete,” J.

of Engr. Mechanics, 1997: 25–35):

Test condition 1 23 4 5 Normal 42.8 55.6 49.0 48.7 44.1 High 90.9 93.1 86.3 90.3 88.5 Test condition 6 7 8 9 10 Normal 55.4 50.1 45.7 51.4 43.1 High 88.1 93.2 90.8 90.1 92.6 Test condition 11 12 13 14 15 Normal 46.8 46.7 47.7 45.8 45.4 High 88.2 88.6 91.0 90.0 90.1

a. Construct a comparative boxplot of peak stresses for the two types of concrete, and comment on any interesting features.

b. Estimate the difference between true average peak stresses for the two types of concrete in a way that conveys information about precision and reliability. Be sure to check the plausibility of any assumptions needed in your analysis.

Does it appear plausible that the true average peak stresses for the two types of concrete are identical? Why or why not?