quiz4_2009

# quiz4_2009 - 6.034 Quiz 4 December 2 2009 Name email Circle...

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6.034 Quiz 4 December 2, 2009 Name email Circle your TA and recitation time (for 1 point) , so that we can more easily enter your score in our records and return your quiz to you promptly. TAs Erica Cooper Matthew Peairs Lisa Fisher Mark Seifter Yuan K. Shen Jeremy Smith Olga Wichrowska Thu Time Instructor 12-1 Gregory Marton 1-2 Berwick/Marton 2-3 Berwick/Marton 3-4 Berwick/Marton Fri Time Instructor 1-2 Randall Davis 2-3 Randall Davis 3-4 Randall Davis Problem number Maximum Score Grader 1 49 2 50 Total 100 There are 10 pages in this quiz, including this one. In addition, tear-off sheets are provided at the end with duplicate drawings and data. As always, open book, open notes, open just about everything. 1

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Problem 1: Bayesian Inference (49 points) Part A: Bayes Nets (30 Points) H Z R M V 0.1 0.2 M H F 0.7 T 0.8 V R F 0.1 T 0.3 M V Z F F 0.01 F T 0.4 T F 0.5 T T 0.6 You decide to use Bayes Nets to help you explain recent sightings of Zombies on campus. In your net you define the following variables: M = A M agical spell was cast { T, F } V = There is a V iral outbreak of H1Z1 {T, F} H = You see a H ippogriff (a magical creature) { T, F } Z = You see a Z ombie { T, F} R = You see Time t R avelers in hazmat suits trying to contain the viral outbreak. {T, F } Using this Bayes Net, answer the following questions: A1 (3 points): What is the probability of NOT seeing a Zombie given that NO magic spell has been cast and there is NO viral outbreak? Write down the probability you are computing and give an numeric answer. 2
A2 (3 points): Joint Probability: What is the probability of the following state of the world? P(M=T, H=T, Z=T, V=T, R=T) Give an expression in terms of the probabilities that can be directly read from the network . You need not compute the final numeric answer.

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