exam2_sp07_stu_answers - Name: _Solution_ Problem #1 (20...

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Name: ___________________ Solution ______________ Problem #1 (20 points total) A company is evaluating the ultimate strength (Su) of two types of cement as it cures over time. Consider the raw data, the best-fit lines, and the r-squared values determined using the method of least-squares for Cement A (A) and Cement B (B) below. Su = 0.0386*Time + 2.0571 0 1 2 3 4 0 1 2 3 4 5 6 Curing Time (h) Ultimate Strength, Su (GPa) Su = 0.6671*Time + 0.5821 0 1 2 3 4 0 1 2 3 4 5 6 Curing Time (h) Cement A: 2 2.25 and 0.388 Su r = = Cement B: 2 2.25 and 0.949 Su r = = 1.1 (4 points) The computed r-squared value for A is much less than that of B because: (Clearly circle one response.) a. The Sum of Squares of Errors (SSE) for A is considerably less than for B b. The Sum of Squares of Errors (SSE) for A is considerably greater than for B c. The Sum of Squares of Deviations (SST) for A is considerably less than for B d. The Sum of Squares of Deviations (SST) for A is considerably greater than for B e. Both B and C 1.2 (8 points) Which of the following statements is/are true? (Circle all that are true.) a. The slope of the regression line for B is greater than the slope of the regression line for A. b. The “goodness of fit” (as measured by r 2 ) of the regression line for B is greater than “goodness of fit” of the regression line for A. c. The value of intercept of the regression line for A is greater than the value of the intercept of the regression line for B. d. The mean Su value for A is equal to the mean Su value for B. 1.3 (4 points) The intercept for Cement B is: (Clearly circle one response) a. 0.75 b. 0.5821 c. 0.6671 d. 0 1.4 (2 points) The r 2 value of B is 0.949. This means that 94.9% of the variation of the data around the regression line is due to unexplained error. (Clearly circle one response) True False 1.5 (2 points) By comparing A and B, we can tell that the regression line for A fits the data for A
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This note was uploaded on 09/14/2009 for the course ENGR 126 taught by Professor Oakes during the Fall '08 term at Purdue University-West Lafayette.

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exam2_sp07_stu_answers - Name: _Solution_ Problem #1 (20...

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