Answer to Question #94677 in Statistics and Probability for kmonte

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.