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Midterm 2A SP10 Solutions

# D all of the above statements are true about a

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d. All of the above statements are true about a continuous random variable. 19. If two events are independent, what is the probability that they both occur? a. 0 b. 0.50 c. 1.00 d. Cannot be determined from the information given 20. Suppose the standard deviation of X equals 4. Then the standard deviation of 2X is equal to which of the following? a.4 b. 2 c.8 d. 16 21. 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. 22. If P(A) = 0.84, P(B) =0.76 and P(A or B) =0.90, then P(A and B) is: a. 0.64 b. 0.70 c. 0.14 d. Can’t tell from the information given. 5

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Problems 23-24. 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. 23. What is the chance that a person in the U.S. has a cell phone? a.16% b. 39% c.32% d. 83% 24. 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? a. .63 10 b. .37 10 c. 1 - .63 10 d. 1 - .37 10 25. It is possible for a relationship that you found between two variables to actually reverse direction if you add a third confounding variable to the mix. a.TRUE b. FALSE 26. Which of the following CANNOT be used to test for independence? a.P(A|B) = P(B) b. P(A|B) = P(A c |B) c.Both a and b can be used to test for independence d. Neither a nor b can be used to test for independence 27. Suppose X is a random variable whose only possible value is 10. Then µ x = 10. a.TRUE b. FALSE 28. Suppose X is a random variable whose only possible value is 10. Then σ x = 10. a.TRUE b. FALSE 29. Suppose you have a deck of 52 cards and you draw one at random. Let A be the event the card is a 2, and let B be the event that the card is red. The events A and B in this situation are independent. a.YES b. NO 30. The variance of X – Y equals the variance of Y- X. a.TRUE b. FALSE Record your final answers to all MC/TF questions 1- 30 on the answer sheet on the last page. That is what we will grade for the MC/TF questions. 6
SHORT ANSWER/SHOW YOUR WORK PROBLEMS (10 PROBLEMS – 5 PTS EACH) Answers without justification, even if correct, may not receive credit. Put your final answer in the blank where provided – NOT ON THE ANSWER SHEET! Problems 31-35. An advertising executive is studying the television (TV) viewing habits of conventional married couples. On the basis of past records, she determined that husbands watch TV 60% of the time. She also determined that when the husband is watching TV, the wife is also watching 40% of the time, and when the husband is not watching TV, the wife is watching TV 30% of the time. H – Husband Watching TV

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d All of the above statements are true about a continuous...

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