SOLUTION: A random sample of 9 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 fo

Question 1159559: A random sample of 9 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:
10, 5, 12, 6, 12, 11, 6, 12, 10
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 places. Round your answers to one decimal place. (If necessary, consult a list of formulas.)
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
You need the mean, the sd, the sample size.
the mean is 9.333
the sd for the sample is 2.872
the sample size is 9
90%CI is mean +/- t(0.95, df=9) s/sqrt(n)
the half-interval is 1.86*2.872/3=1.78
the 90% CI is ($7.55, $11.11)

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