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Answer:
The confidence interval at this level of confidence is between 5.4455 and 12.3545.
Step-by-step explanation:
We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Ztable as such z has a pvalue of .
So it is z with a pvalue of , so
Now, find M as such
In which s is the standard deviation of the sample, which is also called standard error. So
The lower end of the interval is the sample mean subtracted by M. So it is 8.9 - 3.4545 = 5.4455
The upper end of the interval is the sample mean added to M. So it is 8.9 + 3.4545 = 12.3545
The confidence interval at this level of confidence is between 5.4455 and 12.3545.