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homework_7_ans_stud - Course MTH 1210...

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Course MTH 1210 Apr 16’09 Homework #7 (answers) ( Confidence intervals ) Use MS Excel program Three_distributions.xls, sheet 3 and the formula for the confidence interval [see handout #10] _ _ _ x * ± z (1 – α/2) σ x_mean or [ x * – z (1 – α/2) σ x_mean , x * + z (1 – α/2) σ x_mean ] (10.1) _ where x * and σ x_mean are a sample mean and a standard deviation of the sampling distribution of the sample means, respectively, z (1 – α/2) is a reliability factor (coefficient) to solve the problems below. For each of the following exercises construct ( a ) 90, ( b ) 95 , and ( c ) 99 percent confident intervals for the population mean. Using the relations 100(1 – α) = 90, 100(1 – α) = 95, and 100(1 – α) = 99 percent we find that the corresponding values of α are 0.1, 0.05, and 0.01 respectively. Now we run the Excel program Three_distributions.xls , sheet 3 and enter one by one the values of 0.1 , 0.05, and 0.01 in the in the cell I73 . The corresponding values of z (1 – α/2) that appear in the cell K73 are 1.645 , 1.960 , and 2.576 respectively.
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