The Problem

The daily salaries of substitute teachers for 8 local school districts are shown below. Find the 90% confidence interval of the mean for the salaries of substitute teachers in the region.

 \$60 \$56 \$60 \$55 \$70 \$55 \$60 \$55

From the statement of the problem we have n = 8, and the sample standard deviation, s, can be calculated from the data. We are looking for a 90% confidence interval of the mean and n < 30 where the standard deviation is unknown. Thus we use the TI83/84 TInterval function.

Press STAT and then press ENTER to select 1:Edit. Enter the 8 sample values in .

Press STAT and right arrow twice to TESTS. Arrow down to 8:TInterval and press ENTER to select it. If Data is not selected, left arrow and press ENTER to select it. Arrow down once and verify that is entered. Arrow down once and verify that 1 is entered. Arrow down once and type .90 after C-level:.

Arrow down one last time and press ENTER. The calculation will now be preformed, and the results are shown below.

The 90% confidence interval of the mean is 55.47 < < 62.28.

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