Serum Cholesterol Levels. According to the National Health and Nutrition Examination Survey, published by the National Center for Health Statistics, the serum (noncellular portion of blood) total cholesterol level of U.S. females 20 years old or older is normally distributed with a mean of 206 mg/dL (milligrams per deciliter) and a standard deviation of 44.7 mg/dL.

a. Determine the percentage of U.S. females 20 years old or older who have a serum total cholesterol level between 150 mg/dL and 250 mg/dL.

b. Determine the percentage of U.S. females 20 years old or older who have a serum total cholesterol level below 220 mg/dL.

c. Obtain and interpret the quartiles for serum total cholesterol level of U.S. females 20 years old or older.

d. Find and interpret the fourth decile for serum total cholesterol level of U.S. females 20 years old or older.