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sample-m2-09 - Stat 126 Exam 2 Spring 2006 Name ID I pledge...

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Stat 126 Exam 2 Spring 2006 Name: ID#: I pledge that I have neither given nor received unauthorized aid on this exam. Signature: (1) Check “true” or “false”. (a) If X Uniform ( - 3 a, 3 a ), Y Uniform ( - a, a ), then V arX = 3 V arY . true ; false . (b) If X Poisson (1), then 2 X Poisson (2). true ; false . (c) Let X denote the total number of heads among 10 tosses of a coin ( p ), and X and 10 - X have the same distribution. Then p = 1 / 2. true ; false . (d) If the indicators I A and I B satisfy I A I B = 0, then the events A and B are mutually exclusive. true ; false . (e) Let X be the total number of tosses of a coin [with P ( H ) = 3 / 4] right before the 4th tail appears. Then EX = 15. true ; false . (f) If f is the density of X , then f ( x ) = P ( X = x ). true ; false . (g) If X and Y follow geometric distributions with EX > EY , then V arX > V arY . true ; false . 1
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(h) If X Poisson (3), Y Poisson (1), and X and Y are independent, then X - Y Poisson (2). true ; false . (i) If both X and Y follow exponential distributions with EX > EY , then P ( X > 1) > P ( Y > 1).
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