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Unformatted text preview: STAT 100A MIDTERM EXAM Solution Problem 1: Suppose we generate two independent random variables X and Y uniformly over [0 , 1]. (1) (4 points) Calculate P ( X 2 + Y 2 1). A: Let be the unit square [0 , 1] 2 , and let A be the event that X 2 + Y 2 1, then P ( A ) =  A  /   = / 4. (2) (6 points) Calculate P ( X > 1 / 2  X + Y < 1). A: Let A be the event that X > 1 / 2, and let B be the event that X + Y < 1, then P ( A  B ) = P ( A B ) /P ( B ) = (1 / 8) / (1 / 2) = 1 / 4. Problem 2: Suppose at any moment, the probability that there is fire in a particular building is . Given there is fire, the probability that the fire alarm is heard is . Given there is no fire, the probability that the fire alarm is heard is . (1) (5 points) At any moment, what is the probability that we hear the fire alarm? A: P (alarm) = P (fire) P (alarm  fire) + P (nofire) P (alarm  nofire) = + (1 ) ....
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This note was uploaded on 12/16/2008 for the course STATS 100A taught by Professor Wu during the Fall '07 term at UCLA.
 Fall '07
 Wu
 Probability

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