Exercise on the Z Confidence Interval for the Population Mean

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Estimate the mean mpg of all cars with 91% confidence. After collecting a random sample of 41 cars you find a sample mean of 29 miles. Assume the distribution of mpg for all cars is normal with a standard deviation of 4.4 miles.

Directions: Fill in the blanks and click the button to have your answers graded.
A. Do not round intermediate calculations.
B. Round your answers to two decimal places.
C. You have 30 minutes to complete your work before session timeout. After that your work
will not be graded correctly.

1. Z table value =
2. Margin of Error =
3: You estimate with 91% confidence that the population mean falls between
the lower value of
and the upper value of
(If you get Question 3 correct, you will be asked an additional question)

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