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Reading proficiency: An educator wants to construct a 99.5% condence interval for the proportion of elementary school children in Colorado who are proficient in reading. (a) The results of a recent statewide test suggested that the proportion is 0.77. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.07? A sample of E] elementary school children is needed to obtain a 99.5% condence interval with a margin of error of 0.07