Question

In a random sample of 50, the average is 3987 with a population standard deviation of 630. How can one find the 90% confidence interval of the true mean?

Answer 1

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the Z score for .4500 from mean (Z = 1.645)

90% conf. Interval = mean ± 1.645(SD)

Answer 2

z = 50