the level of cholesterol in the blood is important because high cholesterol levels may increase the risk of heart disease. the distribution of blood cholesterol levels in a large population of people of the same age and sex is roughly normal. for 14-year-old boys, the mean is 170 mgs. of cholesterol per deciliter of blood and the standard deviation is 30 mg/dl. levels above 240 may require medical attention. what percent of 14-year-old boys have more than 240 mg/dl of cholesterol?