A survey collects demographic, socioeconomic, dietary, and health-related information on an annual basis. Here is a sample of 20 observations on HDL cholesterol level (mg/dl) obtained from the survey (HDL Is "good" cholesterol; the higher its value, the lower the risk for heart disease). 34 48 53 53 66 50 50 46 87 35 15 34 40 44 40 64 34 31 47 (a) Calculate a point estimate (in mg/dl) of the population mean HDL cholesterol level. mg/dl (b) Making no assumptions about the shape of the population distribution, calculate a point estimate (in mg/dl) of the value that separates the largest 50% of HDL levels from the smallest 50%. mg/dl (c) Calculate a point estimate (in mg/dl) of the population standard deviation. (Round your answer to three decimal places.) mg/dl (d) An HDL level of at least 60 is considered desirable as it corresponds to a significantly lower risk of heart disease. Making no assumptions about the shape of the population distribution, estimate the proportion p of the population having an HDL level of at least 60. P =