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**amma0913** Let A be the event that a patient has cancer. In the course of a hospital stay,

the doctors on duty learn the results of test T1. A little later they learn the results of

test T2. Is it possible that, considered separately, positive results on T1 and T2 might

each increase the chance of A (i.e., P(A|T1) > P(A), and P(A|T2) > P(A)), but that if

both are known to be positive they decrease the chance of A (i.e., P(A|T1; T2) < P(A))?

Explain your answer either with a clear example or in the style of a mathematical

demonstration.