50,000 households. simple random sample of 1000 households whohas to commute to

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50,000 households. simple random sample of 1000 households whohas to commute to work. average commuter drives about 8.7 miles towork with SD distance of 9.0 miles SE ˜285 SE avg ˜ 0.3 average commuter distance is 8.7 miles and likely to be off by0.3 Question: If possible find a 95% confidence interval for theaverage commute distance of all heads of household in town. Answer = 8.7±0.6 miles ------>>> How is it that its 0.6 miles??? Whatwas used to compute the answer to 0.6?? 50,000 households. simple random sample of 1000 households whohas to commute to work. average commuter drives about 8.7 miles towork with SD distance of 9.0 miles SE ˜285 SE avg ˜ 0.3 average commuter distance is 8.7 miles and likely to be off by0.3 Question: If possible find a 95% confidence interval for theaverage commute distance of all heads of household in town. Answer = 8.7±0.6 miles ------>>> How is it that its 0.6 miles??? Whatwas used to compute the answer to 0.6??

Explanation / Answer

SE(avg) = SD/n = 9/1000 = 0.285 To get a 95% confidence interval use z = 2 (or 1.96) pop avg = sample avg +/- 2*SE(avg)     =8.7 +/- 2*(.285) = 8.7 +/- 0.6 Hope this helps, Mike

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