Question 1159553: An existing inventory for a test measuring self-esteem indicates that the scores have a standard deviation of 12. A psychologist gave the self-esteem test to a random sample of 60 individuals, and their mean score was 60 . Construct a 90% confidence interval for the true mean of all test scores. Then complete the table below.
Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.
What is the lower limit of the 90% confidence interval?
What is the upper limit of the 90% confidence interval?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Because the sd is known, this is a z-interval
The interval is the mean+/-z(0.95)*sigma/sqrt(n)
the half-interval or the margin of error is 1.645*12/sqrt(60)
=2.548 or 2.55
(57.45, 62.55) or (57.5, 62.4), the asymmetry being due to rounding.
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