Midterm_2_Sp_11

# The length of bobs trip and whether or not he forgot

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12. The length of Bob’s trip and whether or not he forgot to pack something important are independent. a. TRUE b. FALSE #13-14: Suppose 63% of the U.S. population is annoyed by other people’s cell phone conversations. Of those who are annoyed, only 32% have cell phones. Of those not annoyed, 51% own cell phones. 13. What is the chance that a person in the U.S. has a cell phone? 14. Choose 10 people from the U.S. at random. What is the chance that at least one of them is annoyed by other people’s cell phone conversations?

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15. Bob’s Z-score on an exam is 0.25. What is the correct interpretation? Circle one: a) Bob’s score is .25 points above the mean. b) Bob’s score is at the 25 th percentile. c) Bob’s score is 0.25 standard deviations above the mean. d) Bob got 25% on the exam. 16. If A and B are disjoint events where P(A) = 0.20 and P(B) = 0.30, then P(A and B) equals: a.0.50 b. 0.06 c. 0.00 d. Can’t tell from the information given. 17. Suppose X and Y are independent with X σ = 20; Y σ = 10. What is Y X - σ ? 18. Which of the following needs X and Y to be independent in order to be true? a. The variance of X + Y = variance of X + variance of Y b. The correlation between X and Y equals 0. c. The mean of X+Y = mean of X + mean of Y d. All of these choices require independence in order to be true. 19. Exam scores have a normal distribution with mean of 80 and standard deviation 2. Bob’s score is at the 50 th percentile. This means he scored a 50 on the exam. 20. Ignoring confounding variables can result in Simpson’s Paradox. #21-23: 60% of all customers at a certain fast food restaurant order a hamburger, while 50% of their customers order a Diet Coke. Given that a customer orders a Diet Coke, the chance of them ordering a hamburger is 80%. (There IS enough info to work these pbms. As always, think best about how to set things up before you start.)
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