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 μ = 7950 and estimated standard deviation σ = 2800. 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? (Round your answer to four decimal places.)

(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?
The probability distribution of x is approximately normal with μx = 7950 and σx = 2800.
The probability distribution of x is not normal.
The probability distribution of x is approximately normal with μx = 7950 and σx = 1400.00.
The probability distribution of x is approximately normal with μx = 7950 and σx = 1979.90.

What is the probability of x < 3500? (Round your answer to four decimal places.)

(c) Repeat part (b) for n = 3 tests taken a week apart. (Round your answer to four decimal places.)

(d) Compare your answers to parts (a), (b), and (c). How did the probabilities change as n increased?
The probabilities increased as n increased.
The probabilities stayed the same as n increased.
The probabilities decreased as n increased.

If a person had x < 3500 based on three tests, what conclusion would you draw as a doctor or a nurse?
It would be an extremely rare event for a person to have two or three tests below 3,500 purely by chance. The person probably does not have leukopenia.
It would be a common event for a person to have two or three tests below 3,500 purely by chance. The person probably does not have leukopenia.
It would be an extremely rare event for a person to have two or three tests below 3,500 purely by chance. The person probably has leukopenia.
It would be a common event for a person to have two or three tests below 3,500 purely by chance. The person probably has leukopenia.