5.2.4 The serum cholesterol levels of a population of 12-to 14-year-olds follow a normal
distribution with mean 155 mg/dl and standard deviation 27 mg/dl
What percentage of the 12- to 14-year-olds have serum cholesterol values
between 145 and 165 mg/dl?
Suppose we were to choose at random from the population a large number of
groups of nine 12- to14-year-olds each. In what percentage of the groups
would the group mean cholesterol value be between 145 and 165?
If ? represents the mean cholesterol value of a random sample of nine
12- to 14-year-ols form the population, what is Pr? 145 ? ? ? 165]?