Credit Union Incomes
Credit Union Incomes. Find the 90% confidence interval of the population mean for the incomes of Pennsylvania credit unions. A random sample of 50 credit unions is shown. The data are in thousands of dollars.
Solution: We have the following table:
The population standard deviation is not known, but the sample size is large enough to apply a normal approximation using
as an approximation of
. Therefore, we get that the
interval is approximated as
where
corresponds to the two-tailed z-critical value for
. Hence, we get
This means that there is a probability of that the actual population mean
is contained by the interval
.
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