A pollster wants to construct a 90% confidence interval for the proportion of adults who believe that economic conditions are getting better. (a) A poll taken in July 2010 estimates this proportion to be 0.28 . Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.01 ? A sample of adults is needed to obtain a 90% confidence interval with a margin of error of 0.01 .
Added by Dillon A.
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We know the confidence level is 90%, which means the critical value (z-score) is 1.645 (from the standard normal distribution table). Show more…
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