| The Problem |
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A random sample of 48 days taken at a large hospital shows that an average of 38 patients were treated in the emergency room per day. The standard deviation of the population is 4. Find the 99% confidence interval of the mean number of ER patients treated each day. |
From the statement
of the problem we have n = 48, 
=
38, and 
=
4. We are looking for a 99% confidence interval of the mean, where n
> 30 and the standard deviation is known. Thus, we use the following
TI83/84 ZInterval function.
Press STAT and
right arrow twice to TESTS. Press 7 to select 7:ZInterval.
If Stats is not selected, arrow right and then press ENTER
to select it. Arrow down once and type 4 after :.
Arrow down once and enter 38 after :.
Arrow down once more and type 48 after n:. Arrow down once
and type .99 after C-level:.
Arrow down one last time and press ENTER. The calculation will now be preformed, and the results are shown below.
The 99% confidence
interval of the mean is 36.513 < 
< 39.487.
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