The accompanying table gives summary data on cube strength (N/mm^2) for concrete

Question

The accompanying table gives summary data on cube strength (N/mm^2) for concrete specimens made with a pulverized fuel-ash mix. Calculate a 99% CI for the difference between true average 7-day strength and true average 28-day strength. (Use mu_0: mu_7 - mu_28 = 0.) Interpret your 99% CI With 99% confidence, that the true difference falls above the upper bound. With 99% confidence, that the true difference falls below the lower bound. With 99% confidence, we can say that the true difference falls between these values. With 99% confidence, that the true difference falls outside these values. You may need to use the appropriate table in the Appendix of Tables to answer this question.

Explanation / Answer

The statistical software output for this problem is:

Two sample T confidence interval:
1 : Mean of Population 1
2 : Mean of Population 2
1 - 2 : Difference between two means
(without pooled variances)

99% confidence interval results:

Hence,

99% CI will be:

(-11.35, -6.31)

Difference Sample Diff. Std. Err. DF L. Limit U. Limit 1 - 2 -8.83 0.9631018 132.02606 -11.347144 -6.3128557

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