Question 955660
In a certain town, 50% of the residents own a cellular phone, 40% own a pager, and 20% own both a cellular phone and a pager. What is the probability that a resident owns a cellular phone or a pager? 
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P(cell OR page) = P(cell)+P(page)-P(cell AND page)
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= 0.5 + 0.4 - 0.2 = 0.7
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Cheers,
Stan H.