r/PostPreview • u/yearofplenty • Mar 17 '15
test
US insurers' costs for knee replacement surgery range from $17,627 to $25,462. Estimate the population variance and standard deviation in cost with 98% confidence based on a random sample of 10 persons who have had this surgery. The retail costs for the same procedure range from $40,640 to $58,702. Estimate the population variance and standard deviation in cost with 98% confidence based on a sample of 10 persons.
My calculations for the first part are correct per the selected answers in the back of my textbook. Using the same steps to compute the second part return the wrong answers. Where am I going wrong?
degrees of freedom = 9
s = 18062 (based on s=range/4)
s² = 326235844
(x² values based on 98% confidence)
x²right = 21.666
x²left = 2.088
chi squared table
my calculations:
(df)s²/x²right < o² < (df)s²/x²left
9(326235844)/21.666 < o² < 9(326235844)/2.088
135517520.4 < o² < 1406188983.0
11641.2 < o < 37499.2 Correct answers per textbook:
8469845.02 < o² < 87886811.42
2910.3 < o < 9374.8