Medical: White Blood Cells Let x be a random variable that represents white blood cell count per cubic milliliter of whole blood. Assume that x has a distribution that is approximately normal, with mean m 5 7500 and estimated standard deviation s 51750 (see reference in Problem 15). A test result of x , 3500 is an indication of leukopenia. This indicates bone marrow depression that may be the result of a viral infection.

(a) What is the probability that, on a single test, x is less than 3500?

(b) Suppose a doctor uses the average x for two tests taken about a week apart. What can we say about the probability distribution of x ? What is the probability of x , 3500?

(c) Repeat part

(b) for n 5 3 tests taken a week apart.

(d) Interpretation Compare your answers to parts (a),

(b), and (c). How did the probabilities change as n increased? If a person had x , 3500 based on three tests, what conclusion would you draw as a doctor or a nurse?

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