The critical value used is (10 – 2.5, 10 + 2.5) when, the mean is 10 and confidence level is 89%.
The confidence interval for a population with a known standard deviation is based on the fact that the sample means follow an approximately normal distribution. Suppose
mean = 10
as, we have 89% confidence interval (5, 15)
where EBM = 5.
To get 89% confidence interval,
mean = 10 of the normal distribution.
Then, the critical value we use is
(10 – 2.5, 10 + 2.5).
So, the critical value used is (10 – 2.5, 10 + 2.5) when, the mean is 10 and confidence level is 89%.
Hence, the critical value used is (10 – 2.5, 10 + 2.5) when, the mean is 10 and confidence level is 89%.
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