DQ 4.2. The “Ucountem” research firm selected a random sample of 300 voters. We would like to know the true or real mean average age of the voters. The sample average age was found to be 62, and the sample standard deviation is 5 years. Calculate the 95% confidence interval, showing the confidence limits. Hint, because the sample size is greater than 30, we use the Z factor for 95%. INCLUDE AN EXCEL SPREADSHEET SHOWING YOUR WORK TO CALCULATE THE 95% CONFIDENCE INTERVAL. You can use Excel functions, or show your work manually using the Confidence Interval formula shown on page 306 of the Doane & Seward text. (Formula 8.6).You better look in the text, it does not paste well here. And the text also provides the Z factor for this 95% problem.

(8.6) . x ± z√σ / n

(confidence interval for μ with known σ)

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