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Answer:
The 99% confidence interval for the 1999 mean incomes of Middletown householders is ($33,013.5, $33,892.5).
Step-by-step explanation:
Of the 40,000 persons, 2621 householders reported their income.
The sample size of the study is, <em>n</em> = 2621.
As the sample size is large, i.e. <em>n</em> > 30 use <em>z</em>-distribution to compute the confidence interval.
The confidence interval for mean is:
The mean of this sample is,
The standard deviation is,
The critical value of <em>z</em> for 99% confidence level is:
The 99% confidence interval for the 1999 mean incomes of Middletown householders is:
Thus, the 99% confidence interval for the 1999 mean incomes of Middletown householders is ($33,013.5, $33,892.5).