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Unformatted text preview: Answer. Let D be the families that own a dog, and C the families that own a cat. We are given P ( D ) = . 36 , P ( C ) = . 30 , P ( C  D ) = . 22 We want to know P ( D  C ). We know P ( D  C ) = P ( D C ) / P ( C ). To find the numerator, we use P ( D C ) = P ( C  D ) P ( D ) = ( . 22)( . 36) = . 0792. So P ( D  C ) = . 0792 /. 3 = . 264 = 26 . 4%. Example. Suppose 30% of the women in a class received an A on the test and 25% of the men received an A. The class is 60% women. Given that a person chosen at random received an A, what is the probability this person is a women? Answer. Let A be the event of receiving an A, W be the event of being a woman, and M the event of being a man. We are given P ( A  W ) = . 30 , P ( A  M ) = . 25 , P ( W ) = . 60 and we want P ( W  A ). From the definition P ( W  A ) = P ( W A ) P ( A ) . As in the previous example, P ( W A ) = P ( A  W ) P ( W ) = ( . 30)( . 60) = . 18 ....
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 Spring '09
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