For the serum cholesterol distribution of Exercise 4.3.9, find (a) The 80th percentile (b) The 20th percentile

Question:

For the serum cholesterol of Exercise 4.3.9, find
(a) The 80th percentile
(b) The 20th percentile
Exercise 4.3.9
The serum cholesterol levels of 12- to 14-year-olds follow a normal with mean 155 mg/dl and standard deviation 27 mg/dl.
Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...