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Statistics - Sample size

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A New York Times article about poll results states, "In theory, in 19 cases out of 20, the results from such a poll should differ by no more than one percentage point in either direction from what would have been obtained by interviewing all voters in the United States." Find the sample size suggested by this statement.

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We take p = 0.5. Therefore q = 1 - p = 0.5
19 out of 20 is (19/20) * 100 = ...

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