Exam 1 Practice Test - Stat 212 Exam I Practice 1. A survey...

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Stat 212 Exam I Practice 1. A survey of a random sample of 100 WSU undergraduates revealed that 10 Freshman, 16 Sophomores, 16 Juniors and 18 Seniors owned cell phones. The total numbers of students in each class were: 20 Freshman, 26 Sophomores, 27 Juniors, and 27 Seniors. a) Fill in the contingency table below to reflect cell phone ownership among the undergraduates. F S J Sr Total Total 20 26 27 27 100 b) Estimate the probability that a randomly chosen student owns a cell phone. 60/100 = 0.6 c) Estimate the probability that a randomly chosen student is a freshman. 20/100 = 0.2 d) Estimate the probability that a randomly chosen student owns a cell phone and is a freshman. 10/100 = 0.1 e) Are the events owning a cell phone and being a freshman independent events. Justify your answer. No, because the probability of owning a cell phone and being a freshman does not equal the probability of owning a cell phone times the probability of being a freshman. That is, 0.1 ≠ 0.6 x 0.2 f) Given that a student is a senior, estimate the probability that the student owns a cell phone. 18/27 = 0.667 Cell 60 No Cell 40
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2. Use the following output to answer parts a-e below: a) What is the Slope of the Regression Line? Slope = 0.00256 b) Is the regression equation very useful? Cite a statistic from the output to back up your argument. No, because R-Sq is only 10.4% so only 10.4% of the variation in GPA is explained by knowing Verbal score meaning that about 90% of the variation is not explained. c) Is there a positive or negative linear relationship between Verbal and GPA? Cite evidence from the output above. Positive because slope is positive (0.00256) d) Interpret the slope of the regression line. For each one unit increase in verbal score, there is a 0.00256 increase in GPA. e) What is the Correlation coefficient? 3. For the Regression Equation: Y = 5 + 2X a) Find the predicted Y for X=10 Y-hat = 5 + 2 (10) = 25 b) What is the residual for the data point (Y=15, X=6)? Y-hat = 5 + 2 (6) = 17 Residual = Y – Y-hat = 15 – 17 = -2 The regression equation is GPA = 1.11 + 0.00256 Verbal r 2 = 10.4%
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4. The Sample Standard Deviation is a “rough” estimate of the average distance between what? The average distance between the observations and their mean 5. The Math SAT scores for the seniors at a high school were collected for a study. An overall mean for all the scores was calculated and the scores were found to fall into a bell-shaped distribution. One of the seniors, named Bob, had a score of 720. a)
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This note was uploaded on 02/15/2012 for the course STATS 212 taught by Professor Staff during the Fall '08 term at Washington State University .

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Exam 1 Practice Test - Stat 212 Exam I Practice 1. A survey...

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