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Test 3 Spring 2011

# Test 3 Spring 2011 - 1 An environmentalist would like to...

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1. An environmentalist would like to study the relationship between home energy usage and the number of occupants. What would you expect regarding the correlation between the cost of home energy usage and the number of occupants? B a. Negative correlation b. Positive correlation c. Close to 0 correlation d. Correlation cannot be computed 2. Which of the following correlation coefficients represents the strongest relationship? C ______________________________________________________________________ ________ QUESTIONS 3 - 4: The number of firefighters it takes to control a fire has a strong, linear, positive association (r = 0.79) with the size of the fire. 3. Which variable is the explanatory variable? 4. Which statement best interprets the correlation coefficient, r = 0.79, in this context? increases ______________________________________________________________________ ________ MSIT 3000 Test 3 Version 1 Page 1

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QUESTIONS 5 - 9 : To help make a decision about possible replacement of aging welding equipment used in a manufacturing process, you collected data on repairs costs (in hundreds of dollars) and age of the welding machine (in months) for 37 machines. Graphs and statistics support the appropriateness of the linear regression model: · Repair Cost = 5.38+ 2.47 Age 5. To test whether the simple linear model is useful, we test a. Whether the y-intercept is different from 0. b. Whether the y-intercept is different from 1. c. Whether r 2 is large. d. Whether the slope parameter is different from 0. e. Whether the slope parameter is different from 1. 6. Which of the following is a correct interpretation of the slope parameter estimate? a. As age increases by 1 month, repair costs increase on average by \$538. b. As repair costs increase by \$100, the machines are aging on average by 2.47 months. c. As repair costs increase by \$247, the machines are 2.47 months older. d. As age increases by 1 month, repair costs increase on average by \$247. e. When Age is 0, repair costs are predicted to be \$247 during that month on average.
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