Midterm 2A1 SP10 Solutions

# Suppose we know bob went on a long trip what is the

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16. Suppose we know Bob went on a long trip. What is the chance that he forgot to pack something important? a. 0.60 b. 0.80 c. 0.75 d. None of the above 17. Whether or not Bob forgot something important is INDEPENDENT of length of his trip. 18. What can we tell from the probabilities in the above table? a. Bob forgets something important just as often when he takes a short trip compared to a long trip. b. Bob forgets something important more often when he takes a short trip compared to a long trip. c. Bob forgets something important less as often when he’s on a short trip as he does on a long trip. 19. The mean of a random variable X can never be negative. 20. Suppose the standard deviation of X equals 4. Then the standard deviation of 2X is equal to which of the following? a.2 b. 4 c.8 d. 16 21. If two events are independent, what is the probability that they both occur? 22. Which of the following is not true about a continuous random variable? a. The probability of a single value of X is 0. b. Probabilities are found by finding areas under a curve over specified intervals. c. Values of the density function, f(x), must always be between 0 and 1, for all x. d. All of the above statements are true about a continuous random variable. 23. If A and B are disjoint events where P(A) = 0.20 and P(B) = 0.30, then P(A and B) equals: 5

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24. If P(A) = 0.84, P(B) =0.76 and P(A or B) =0.90, then P(A and B) is: Problems 25-26. 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. 25. What is the chance that a person in the U.S. has a cell phone? a.83% b. 39% c.32% d. 16% 26. 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? 27. 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
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