Cholesterol is a fatty substance that is an important part of the outer lining (membrane) of cells in the body of animals. Its normal range for an adult is 120 - 240 mg/dl. The Food and Nutrition Institute of the Philippines found that the total cholesterol level for Filipino adults has a mean of 159.2 mg/dl and 83% of adults have a cholesterol level less than 200 mg/dl. Suppose that the total cholesterol level is normally distributed. (a) Determine the standard deviation of this distribution.