Midterm 2A SP10 Solutions

# What is the new average salary after the raise a

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1. What is the new average salary after the raise? a. .10(\$80,000) b. 1.10(\$80,000) c. \$80,000 because the mean doesn’t change d. None of the above 2. What is the standard deviation of the new salaries after the raise? 3. If A and B are independent events with P ( A ) = 0.20 and P ( B ) = 0.60, then P (A|B) is: 4. P(A|B) + P(A|B c ) = 1 a. True b. False 5. If P ( A ) = 0.25 and P ( B ) = 0.65, then P ( A and B ) must equal 0.25 x 0.65 = .1625. a.Yes b. No 6. A and A c are disjoint events. a. True b. False 7. Suppose the variance of X equals 3 and the variance of Y equals 2. Suppose also that X and Y are independent. Then the variance of X - Y equals 3 – 2 = 1. 8. The cells within a two-way table represent conditional probabilities. a.TRUE b. FALSE 9. Suppose X and Y are independent. Then the standard deviation of X+Y equals the standard deviation of X plus the standard deviation of Y. 3

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Problems 10-11. The distribution of blood types looks like the following. Select two people at random. Call them Bob and Bill. Blood type O A B AB Probability 0.45 0.40 0.11 0.04 10. What is the chance that Bob has type A blood and Bill has type B blood? 11. What is the chance that exactly one of them has type A blood? a.0.40 b. .40(.60) = .24 c..40(.60)(2) = .48 d. None of the above 12. Suppose 25% of students have an iPod. You take a random sample of 2 students. What is the chance that neither one of them owns an iPod? a.0.50 b. 0.56 c.0.44 d. None of these. 13. Which of the following statements is FALSE? Problems 14-16. Bob is planning a trip to visit his cousin in Chicago. We compare the length of his trip (short or long) to whether or not he’ll forget to pack something important. Short trip Long trip Forgot something important 0.20 0.60 Didn’t forget something important 0.05 0.15 14. Whether or not Bob forgot something important is INDEPENDENT of length of his trip. a.TRUE b. FALSE 15. 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 4
d. None of the above 16. What can we tell from the probabilities in the above table? a. Bob forgets something important more often when he takes a short trip compared to a long trip. b. Bob forgets something important less often when he takes a short trip compared to a long trip. c. Bob forgets something important just as often when he’s on a short trip as he does on a long trip.

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