SOLUTION: Find 80%, 85% and 99.9% confidence interval for the sample mean of a population, if we know that in a random sample of 70 people from the population, the sample mean is 60 and the

Question 1183701: Find 80%, 85% and 99.9% confidence interval for the sample mean of a population, if we know that in a random sample of 70 people from the population, the sample mean is 60 and the standard deviation is 5.
Answer by robertb(5830) (Show Source): You can put this solution on YOUR website!
The 99.9% C.I. is worked out as follows:

= [57.946, 62.054]

The t-statistic (with d.f. = 69) was used in the construction of the C.I. since technically, no matter what the sample size is,
as long as the standard deviation of the underlying population is UNKNOWN, the appropriate distribution to use is t.

Now you can do the intervals with 80% and 85% confidence levels.

(t-probabilities were taken from https://stattrek.com/online-calculator/t-distribution.aspx.)
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