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Unformatted text preview: Chapter 7: Random Variables Use the following to answer questions 12: A psychologist studied the number of puzzles subjects were able to solve in a fiveminute period while listening to soothing music. Let X be the number of puzzles completed successfully by a subject. The psychologist found that X had the following probability distribution: Value of X 1 2 3 4 Probability 0.2 0.4 0.3 0.1 1. Referring to the information above, the probability that a randomly chosen subject completes at least three puzzles in the fiveminute period while listening to soothing music is A) 0.3. B) 0.4. C) 0.6. D) 0.9. Ans: B Section: 7.1 Discrete and Continuous Random Variables 2. Referring to the information above, P ( X < 3) has value A) 0.3. B) 0.4. C) 0.6. D) 0.9. Ans: C Section: 7.1 Discrete and Continuous Random Variables Use the following to answer questions 35: Let the random variable X be a random number with the uniform density curve given below. 3. Referring to the information above, P ( X = 0.25) is A) 0.00. B) 0.25. C) 0.75. D) 1.00. Ans: A Section: 7.1 Discrete and Continuous Random Variables Page 98 Chapter 7: Random Variables 4. Referring to the information above, P ( X 0) has value A) 0.0. B) 0.1. C) 0.5. D) 1.0. Ans: A Section: 7.1 Discrete and Continuous Random Variables 5. Referring to the information above, P (0.7 < X < 1.1) has value A) 0.30. B) 0.40. C) 0.60. D) 0.70. Ans: A Section: 7.1 Discrete and Continuous Random Variables 6. Suppose there are three balls in a box. On one of the balls is the number 1, on another is the number 2, and on the third is the number 4. You select two balls at random and without replacement from the box and note the two numbers observed. The sample space S consists of the three equally likely outcomes {(1, 2), (1, 3), (2, 3)}. X , the total of the two balls selected, has probabilities X 3 4 5 Probability 1/3 1/3 1/3 The probability that X is at least 4 is A) 0. B) 1/3. C) 2/3. D) 1.0. Ans: C Section: 7.1 Discrete and Continuous Random Variables Use the following to answer questions 79: The probability density of a random variable X is given in the figure below. 7. Referring to the information above, from this density, the probability that X is between 0.5 and 1.5 is A) 1/3. B) 1/2. C) 3/4. D) 1. Ans: B Section: 7.1 Discrete and Continuous Random Variables 8. Referring to the information above, the probability that X is at least 1.5 is A) 0. B) 1/4. C) 1/3. D) 1/2. Ans: B Section: 7.1 Discrete and Continuous Random Variables Page 99 Chapter 7: Random Variables 9. Referring to the information above, the probability that X = 1.5 is A) 0. B) 1/4. C) 1/3. D) 1/2. Ans: A Section: 7.1 Discrete and Continuous Random Variables 10. A random variable is A) a hypothetical list of the possible outcomes of a random phenomenon....
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This note was uploaded on 03/30/2008 for the course STAT 155 taught by Professor Unknown during the Spring '07 term at UNC.
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