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Answer:
a) The critical value is .
b) The 99% confidence interval for the mean repair cost for the TVs is ($66.31, $110.61).
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 . This is our critical value
So it is z with a pvalue of , so
a. Find the critical value that should be used in constructing the confidence interval.
The critical value is .
b. Construct the 99% confidence interval. Round your answer to two decimal places.
Now, find M as such
In which is the standard deviation of the population and n is the size of the sample. So, in this problem
The lower end of the interval is the mean subtracted by M. So it is 88.46 - 22.15 = $66.31
The upper end of the interval is the mean added to M. So it is 88.46 - 22.15 = $110.61
The 99% confidence interval for the mean repair cost for the TVs is ($66.31, $110.61).