Concept
How do you calculate the probability that a winner is a UMW student or a junior?
Stephen Davies, Ph.D. Version 2.2.2 Through Discrete Mathematics A Cool Brisk Walk / Chapter 1
"winner is from UMW or a junior (or both)? This is Pr( U ∪ J ), which is the probability that the winner is a junior or a UMW student (or both). This calls for computing Pr( U ) plus Pr( J ), but don’t forget to then subtract Pr( U ∩ J ) so we don’t double-count Ben! The correct answer is .7 + .4 - .1, which is equal to 1 . If this surprises you, look again at the data and realize that every swimmer is either a UMW student (Chad and Grover), a junior (Tim), or both (Ben)."
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