Calculating a Confidence Interval for the Mean
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Given Data | Given Statistics

1. Given Data:

Find the 99% confidence interval for the mean using the following data:

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First enter the data in by pressing STAT and selecting 1:Edit by pressing ENTER. The result is shown below

Next press STAT, then RIGHT ARROW twice to TESTS. Press 8 to select 8:TInterval. Data is already highlighted (if not, use LEFT ARROW to highlight it), so press ENTER to select the data mode. Make sure the defaults of for List: and 1 for Freq: are also listed.

 
 
 

ARROW DOWN to C-LEVEL:. Enter the confidence interval as a decimal fraction: .99 Then ARROW DOWN once to Calculate and press ENTER. The results are shown below.

 
 

The final screen reports not only the confidence interval of the mean of (10.593, 24.607) in interval notation, but also the mean and standard deviation of the sample data. The confidence interval of the mean,, of (10.593, 24.607) can also be written as 10.593 < < 24.607.


2. Given Statistics.

Find the 90% confidence interval of the mean when = 182, = 8, and n = 20.

Press STAT, then RIGHT ARROW twice to TESTS. Press 7 to select 7:ZInterval. Data is highlighted.

 
 
 

ARROW RIGHT once to Stats and press ENTER. Stats is now highlighted. ARROW DOWN once and enter 182 for . ARROW DOWN once and enter the value of 8 for , then ARROW DOWN once again, and enter 20 for n.

 
 
 

ARROW DOWN once to C-Level and enter 90% as the decimal .9. ARROW DOWN one last time to Calculate and then press ENTER. The results are shown below.

 
 

The resulting confidence interval of the mean,, in interval notation is (178.91, 185.09), or 178.91 < < 185.09

 



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