Question 765561
Suppose that 47% of all Americans have flown in an airplane at least once and that 28% of all Americans have ridden on a train at least once. 
What is the probability that a randomly selected Americans has either ridden on a train or flown in an airplane?
 Can this problem be solved?
Ans: Only if you assume that no one who flew also rode on a train.
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Under what conditions can it be solved? 
If no one who flew, rode on a train.
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If the problem cannot be solved, What information is needed to make it solvable?
Aswered above.
Cheers,
Stan H.
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