4 The serum cholesterol levels of a certain population of bo

4. The serum cholesterol levels of a certain population of boys follow a normal distribution with mean 176 mg/dl and standard deviation 30 mg/dl. What percentage of the boys have serum cholesterol values

(a) What is the 80th percentile, denoted by X_0.2?

Solution

Using cdf table, if Area(z) = 0.7995 (close to 0.8) then z = 0.84.

y = m + sz = 176 + 30