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Unformatted text preview: College of Human Ecology Cornell University Ithaca, New York Department of Policy Analysis and Management PAM 2100 Intro Stats A. Sinan ¨ Un¨ur – Fall 2008 Prelim 1 – Answer October 2, 2008 Multiple Choice MC 1) Suppose you are told that the average score on the fall semester PAM 2100 prelim was 18 points and there were 50 students in the class. Then, you can be certain that ( a ) The number of students who scored lower than 18 points on the exam is equal to the number of students who scored higher than 118 18 points. ( b ) The sum of all students’ scores is 900. ( c ) Most students scored 18 points on the exam. ( d ) The difference between the highest and lowest score is 10 points. Answer : 1b . ∑ x i 50 = 18 ⇒ ∑ x i = 900 . MC 2) For a research project involving human participants to be approved by the Institutional Review Board at Cornell University, participants must be able to withdraw from the study without penalty. ( a ) never ( b ) occasionally ( c ) usually ( d ) always Answer : 2d . There is no valid reason for forcing participants to stay in a study that might make them uncomfortable or even harm them. MC 3) Consider data on the fuel efficiency of 40 car models. Suppose Q 1 = 20 mpg and Q 2 = 32 Q 3 = 32 mpg. Which one of the following statements is correct? ( a ) 50% of the cars get better than 20 mpg. ( b ) 50% of the cars get between 20 mpg to 32 mpg. ( c ) 50% of the cars get better than 32 mpg. ( d ) 50% of the cars get less than 32 mpg. Answer : 3b . 25% of cars get less than 20 mpg and 25% of cars get better than 32 mpg. Therefore, 50% of cars get between 20 mpg to 32 mpg. MC 4) According to the Census Bureau, the median earnings of male workers 25 and older in the U.S. was $41,539 in 2007. In the same year, average earnings for the same group of workers was $54,966. Based on this information, you can conclude that: ( a ) The distribution of earnings has a longer right tail (is skewed to the right). ( b ) The distribution of earnings is symmetric. ( c ) The distribution of earnings has a longer left tail (is skewed to the left). ( d ) Earnings are normally distributed. Answer : 4a . This is the correct answer among all the answers given (implicitly assumes that the distribution is unimodal). MC 5) Assume that the speed at which people drive on I81 is normally distributed. Suppose you are pulled over while driving at 80 mph on I81. The state trooper tells you the while the average driver obeys the speed limit of 65 mph, 16% drive faster than you. What is the approximate standard deviation of the distribution of speeds at which people drive on I81? ( a ) 25 mph ( b ) 20 mph ( c ) 15 mph ( d ) 10 mph Answer : 5c Looking at the normal distribution, we note that a zscore of approximately 1 corresponds to a right tail probability of 16%. Therefore, we have 80 65 s ≈ 1 ....
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This note was uploaded on 10/16/2008 for the course PAM 2100 taught by Professor Abdus,s. during the Fall '08 term at Cornell University (Engineering School).
 Fall '08
 ABDUS,S.
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