Solved: Concrete As concrete cures, it gains strength. The following data represent the

Chapter 14, Problem 15

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Concrete As concrete cures, it gains strength. The following data represent the 7-day and 28-day strength (in pounds per square inch) of a certain type of concrete: 7-Day Strength, x 28-Day Strength, y 7-Day Strength, x 28-Day Strength, y 2300 4070 2480 4120 3390 5220 3380 5020 2430 4640 2660 4890 2890 4620 2620 4190 3330 4850 3340 4630 (a) Treating the 7-day strength as the explanatory variable, x, determine the estimates of b0 and b1. (b) Compute the standard error of the estimate. (c) Determine whether the residuals are normally distributed. (d) If the residuals are normally distributed, determine sb1 . (e) If the residuals are normally distributed, test whether a linear relation exists between 7-day strength and 28-day strength at the a = 0.05 level of significance. (f) If the residuals are normally distributed, construct a 95% confidence interval for the slope of the true least-squares regression line. (g) What is the estimated mean 28-day strength of this concrete if the 7-day strength is 3000 psi?