The serum cholesterol levels for men in one age group are normally distributed with a mean of 178.2 and a standard deviation of 40.8. All units are in mg/100 mL. Find the 9th percentile.

Question

mathmale · Answer

think of percentile as an area, that is, a certain area under the standard normal curve.

I trust you have a table of z-scores available and know how to use it.

Use the page of the z-score table on which the z-scores are negative.

Find the z-score corresponding to an area under the std. normal curve that is closest to 0.09 (the decimal equivalent of 9%).

What is this z-score?

anonymous · Answer

z score is -1.34

mathmale · Answer

Now find the actual serum level that corresponds to a z-score of -1.34.

$$z=\frac{ x-\mu }{ \sigma } $$

mathmale · Answer

You already know the values of the mean and standard deviation, as well as the z-score.

anonymous · Answer

is it 123.528 or 123.53 mg/100mL???