SME_8e_Ch_07_Section_2

# SME_8e_Ch_07_Section_2 - 1 CHAPTER 7 SECTION 2 RANDOM...

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Unformatted text preview: 1 CHAPTER 7 SECTION 2: RANDOM VARIABLES AND DISCRETE PROBABILITY DISTRIBUTIONS MULTIPLE CHOICE 68. If X and Y are random variables, the sum of all the conditional probabilities of X given a specific value of Y will always be: a. 0.0 b. 1.0 c. the average of the possible values of X. d. the average of the possible values of Y. ANS: B PTS: 1 REF: SECTION 7.2 69. A statistical measure of the strength of the relationship between two random variables X and Y is referred to as the: a. expected value b. variance c. covariance d. standard deviation ANS: C PTS: 1 REF: SECTION 7.2 70. If X and Y are random variables with E ( X ) = 5 and E ( Y ) = 8, then E (2 X + 3 Y ) is: a. 34 b. 13 c. 18 d. 40 ANS: A PTS: 1 REF: SECTION 7.2 71. If X and Y are any random variables with E ( X ) = 5, E ( Y ) = 6, E ( XY ) = 21, V ( X ) = 9 and V ( Y ) = 10, then the relationship between X and Y is a: a. strong positive relationship b. strong negative relationship c. weak positive relationship d. weak negative relationship ANS: B PTS: 1 REF: SECTION 7.2 72. The covariance of two variables X and Y : a. must be between - 1 and +1. b. must be positive. c. can be any real number. d. None of these choices. ANS: C PTS: 1 REF: SECTION 7.2 2 73. If X and Y are any random variables with COV( X , Y ) = 0.25, x 2 = 0.36, and y 2 = 0.49, then the coefficient of correlation is a. 1.417 b. 1.190 c. 0.595 d. 0.354 ANS: C PTS: 1 REF: SECTION 7.2 74. If X and Y are independent random variables, which of the following identities is false? a. COV( X , Y ) = 1 b. E ( X + Y ) = E ( X ) + E ( Y ) c. V ( X + Y ) = V ( X ) + V ( Y ) d. All of these choices are true. ANS: A PTS: 1 REF: SECTION 7.2 TRUE/FALSE 75. Bivariate distributions provide probabilities of combinations of two variables. ANS: T PTS: 1 REF: SECTION 7.2 76. If X and Y are independent variables with V ( X ) = 23.48 and V ( Y ) = 36.52, then the standard deviation of W = X + Y is w = 7.746. ANS: T PTS: 1 REF: SECTION 7.2 77. If X and Y are independent variables, then COV( X , Y ) &amp;gt; 0. ANS: F PTS: 1 REF: SECTION 7.2 78. If X and Y are independent variables, then their coefficient of correlation = 0. ANS: T PTS: 1 REF: SECTION 7.2 79. If X and Y are two variables with x 2 = 12.25, y 2 = 17.64, and COV( X , Y ) = 11.76, then the coefficient of correlation = 0.8. ANS: T PTS: 1 REF: SECTION 7.2 80. If X and Y are two variables with E ( XY ) = 10.56, E ( X ) = 4.22, and E ( Y ) = 5.34, then COV( X , Y ) = 1.0. ANS: F PTS: 1 REF: SECTION 7.2 81. If X and Y are two variables with x = 3.8, y = 4.2, and COV( X , Y ) = - 0.25, then V ( X + Y ) = 31.58. ANS: T PTS: 1 REF: SECTION 7.2 3 82. If X and Y are two variables with x 2 = 3.25, y 2 = 5.8, and COV( X , Y ) = 14.703, then the coefficient of correlation = 0.78....
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SME_8e_Ch_07_Section_2 - 1 CHAPTER 7 SECTION 2 RANDOM...

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