Question

1. White blood cell counts per cubic millimeter of whole blood approximately
follow the Normal Distribution with mean 7500 and standard deviation 1750.
The lowest 2% of all WBC counts are defined to be probable risks. How low
must one’s WBC count be to fall into the at-risk group?

Answer 1

Solution:

For a random variable X:

$X=µ+Zσ$ , where Z is a z-value of standard normal distribution for a desired percentile

From the statistical tables, 2nd percentile has z-value of -2.05. Therefore:

$X=7500-2.05×1750=3912.5$

Answer: 3912.5 cells per cubic millimeter.