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12 M 14 15 16 11iW 19ed Next Previous Question 20 of 20 (1 point) View.problem in a.pop up How's the economy? A pollster wants to construct a 99% 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 0.32. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.02? adults is needed to obtain a 99% confidence interval with a margin of A sample of error of 0.02.

Explanation / Answer

Z for 99% CI is 2.56 ( this we ontani from Z tables)

p estimate = .32

Let n be the sample size we use

MOE = .02

MOE = .02 <= Z*sqrt( p*p'/n)

.004 <= 2.56^2*( .32*.68/n)

Therefore, n > 2.56*(.32*.68)/.004 = 139.264 or n = 139.264 or 140 in integer terms

n = 140 is the right answer

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