The article Mechanical Grading of Oak Timbers (D. Kretschmann and D. Green, Journal of Materials in Civil

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The article "Mechanical Grading of Oak Timbers" (D. Kretschmann and D. Green, Journal of Materials in Civil Engineering, 1999:91-97) presents measurements of the ultimate compressive stress, in MPa, for green mixed oak 7 by 9 timbers from West Virginia and Pennsylvania. For 11 specimens of no. 1 grade lumber, the average compressive stress was 22.1 with a standard deviation of 4.09. For 7 specimens of no. 2 grade lumber, the average compressive stress was 20.4 with a standard deviation of 3.08. Can you conclude that the mean compressive stress is greater for no. 1 grade lumber than for no. 2 grade?
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