# 11_30_09ans - STAT 409 1 Fall 2009 Examples for A...

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Examples for 11/30/2009 Fall 2009 1. A statistics instructor teaches two statistics classes, one in the morning and one in the afternoon. Suppose the probability that the instructor gives a good morning lecture is 0.3. If the morning lecture is good, then the afternoon lecture is also good with probability 0.70. However, if the morning lecture is bad, then there is an 80% chance that the afternoon lecture will also be bad. M = {good morning lecture}, A = {good afternoon lecture}. P( M ) = 0.30 (the probability that the instructor gives a good morning lecture is 0.3) P( A | M ) = 0.70 (if the morning lecture is good , then the afternoon lecture is also good with probability 0.70) P( A ' | M ' ) = 0.80 (if the morning lecture is bad , then there is an 80% chance that the afternoon lecture will also be bad) a) What proportion of the afternoon lectures are bad? P( A ' ) = P( M A ' ) + P( M ' A ' ) = P( M ) P( A ' | M ) + P( M ' ) P( A ' | M ' ) = 0.30 0.30 + 0.70 0.80 = 0.09 + 0.56 = 0.65 . OR

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## This note was uploaded on 10/12/2011 for the course STATISTICS stat 410 taught by Professor Stepanov during the Spring '11 term at University of Illinois, Urbana Champaign.

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11_30_09ans - STAT 409 1 Fall 2009 Examples for A...

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