10.26 The data in represent the compressive strength, in thousands of pounds per
ID: 3384901 • Letter: 1
Question
10.26 The data in represent the compressive
strength, in thousands of pounds per square inch (psi), of 40 samples of concrete taken two and seven days after pouring. Source: Data extracted from O. Carrillo-Gamboa and R. F. Gunst,
“Measurement-Error-Model Collinearities,” Technometrics, 34, 1992,
pp. 454–464.
a. At the 0.01 level of significance, is there evidence that the mean strength is lower at two days than at seven days?
b. What assumption is necessary about the population distribution in order to perform this test?
c. Find the p-value in (a) and interpret its meaning.
Sample Two Days Seven Days
1 2.83 3.505
2 3.295 3.43
3 2.71 3.67
4 2.855 3.355
5 2.98 3.985
6 3.065 3.63
7 3.765 4.57
8 3.265 3.7
9 3.17 3.66
10 2.895 3.25
11 2.63 2.85
12 2.83 3.34
13 2.935 3.63
14 3.115 3.675
15 2.985 3.475
16 3.135 3.605
17 2.75 3.25
18 3.205 3.54
19 3 4.005
20 3.035 3.595
21 1.635 2.275
22 2.27 3.91
23 2.895 2.915
24 2.845 4.53
25 2.205 2.28
26 3.59 3.915
27 3.08 3.14
28 3.335 3.58
29 3.8 4.07
30 2.68 3.805
31 3.76 4.13
32 3.605 3.72
33 2.005 2.69
34 2.495 3.23
35 3.205 3.59
36 2.06 2.945
37 3.425 4.03
38 3.315 3.685
39 3.825 4.175
40 3.16 3.43
Explanation / Answer
10.26 The data in represent the compressive strength, in thousands of pounds per
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