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Hosted by ALEKS Corp. Chapter 8 Quiz Previous1 23 4 5 6 7 89 10 Next Question 9 of 11 (2.5 points) View problem in a pop-up How's the economy? A pollster wants to construct a 99.5% confidence interval for the proportion of adults who believe that economic conditions are getting better. Part 1 out of 2 A poll taken in July 2010 estimates this proportion to be 0.35. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.04? A sample of error of 0.04 adults is needed to obtain a 99.5% confidence interval with a margin of NEXT 18

Explanation / Answer

p = 0.35

Z for 99.5% = Z0.0025 = 2.81

Margin of error = 0.04

Or, Z0.0025 * sqrt(p * (1-p) / n) = 0.04

Or, 2.81 * sqrt(0.35 * 0.65/n) = 0.04

Or, n = 1122.73

Or, n = 1123

Sample size required is 1123

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