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Confidence interval for population mean: T-distribution

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A random sample of 18 health maintenance organizations(HMOs) was selected. For each HMO, the co-payment(in dollars for a doctor's office visit was recorded. The results are as follows:

6, 12, 7,7,11,9,5,10,12,9,11,12,8,8,5,7,5,8.

See the attached file for further details.

Under the assumption that co-payment amounts are normally distributed, find a 90% confidence interval for the mean co-payment amount in dollars.Then complete the table below.
Carry your intermediate computations to at least three decimal placed. Round your answers to one decimal place.

What is the lower limit of the confidence interval?
What is the upper limit of the confidence interval?

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Construction of confidence interval for population mean is discussed in the answer. Excel template for each problem is also included (see attachment). This template can be used to obtain the answers of similar problems.

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