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We do not have the population standard deviation σ, so we will use TInterval.
Press the STAT key.
Press the ► key twice to highlight TESTS.
Press the number 8 key.
We do not have the data itself, so we will select Stats. We enter 15,528 for Ë, 4200 for s
x
, 400
for n, and .99 for the C-Level.
Select Stats for Inpt: and press the ENTER key.
Type in 15528 for Ë.
Type in 4200 for Sx.
Type in 400 for n.
Type in .99 for C-Level.
Highlight Calculate and press the ENTER key.
The TInterval output shows the 99% confidence interval
along with the sample mean, standard deviation, and
sample size.
The 99% confidence interval is from 14984 and 16072.
This says that with 99% confidence we believe that the
true population mean price is between
$14984 and 16072.
Confidence Intervals for Population Proportions
The function 1-PropZInt computes Z-based confidence intervals for a population proportion
where the sample size is large enough, i.e., where both the number of successes and the number
of “failures” are both over five. It is found on the STAT page under the TESTS list. To use 1-
PropZInt, enter in the number of successes as x, the sample size as n, and the confidence level as
C-Level.
Note: x must be a whole number. If you are finding x by multiplying ê by n, you will need to
round to the nearest whole number.
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