Midterm 2A

# Those are the only answers we will grade 1 if a and b

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THOSE ARE THE ONLY ANSWERS WE WILL GRADE. 1. If A and B are disjoint then P(A|B) equals 0. a. TRUE b. FALSE 2. One can show that P(A)P(B|A) = P(B)P(A|B). a. TRUE b. FALSE 3. The branches on a tree diagram contain marginal and conditional probabilities; they do not contain “and” probabilities. a. TRUE b. FALSE 4. The cells in a table represent conditional probabilities. a. TRUE b. FALSE For Questions 5-7: Suppose Bob is planning a trip to visit his cousin in Chicago. We want to 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 0.80 Didn’t forget something important 0.05 0.15 0.20 0.25 0.75 1.00 5. If you calculated 0.20 / 0.80 = 0.25 this number would represent: 6. According to the table above, whether or not Bob forgets something important is independent of the length of his trip. 7. Bob goes on more long trips than short trips. a. TRUE b. FALSE 8. If X and Y are independent, the standard deviation of X + Y equals the standard deviation of X plus the standard deviation of Y. 9. If X and Y are independent, the variance of X – Y equals the variance of Y – X. a. TRUE b. FALSE 3

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10. The mean of a random variable can never be negative. 11. If P(A) = 0.50, P(B) = 0.30, and P(A and B) = 0.15, then A and B are independent. 12. Suppose the percentage of Corvette owners who are women is 25% and the percentage of Corvette owners who are men is 75%. True or False: Corvette ownership is independent of gender.
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