Serum Cholesterol Levels. Information on serum total cholesterol level is published by the Centers for Disease Control and Prevention in National Health and Nutrition Examination Survey.

A simple random sample of 12 U.S. females 20 years old or older provided the following data on serum total cholesterol level, in milligrams per deciliter (mg/dL).

260 289 190 214 110 241 169 173 191 178 129 185

a. Obtain a normal probability plot of the data.

b. Based on your result from part (a), is it reasonable to presume that serum total cholesterol level of U.S. females 20 years old or older is normally distributed? Explain your answer.

c. Find and interpret a 95% confidence interval for the mean serum total cholesterol level of U.S. females 20 years old or older. The population standard deviation is 44.7 mg/dL.

d. In Exercise 6.98, we noted that the mean serum total cholesterol level of U.S. females 20 years old or older is 206 mg/dL. Does your confidence interval in part

(c) contain the population mean?

Would it necessarily have to? Explain your answers.

Extending the Concepts and Skills