Each of 500 soldiers in an army company independently has a certain disease with probability 1 10 3 . This disease will show up in a blood test, and to facilitate matters, blood samples from all 500 soldiers are pooled and tested, a. What is the (approximate) probability that the blood test will be positive (that is, at least one person has the disease)? Suppose now that the blood test yields a positive result. b. What is the probability, under this circumstance, that more than one person has the disease? Now, suppose one of the 500 people is Jones, who knows that he has the disease. c. What does Jones think is the probability that more than one person has the disease? Because the pooled test was positive, the authorities have decided to test each individual separately. The first i -1 of these tests were negative, and the with one—which was on Jones—was positive. d. Given the preceding scenario, what is the probability, as a function of i, that any of the remaining people have the disease?
Each of 500 soldiers in an army company independently has a certain disease with probability 1 10 3 . This disease will show up in a blood test, and to facilitate matters, blood samples from all 500 soldiers are pooled and tested, a. What is the (approximate) probability that the blood test will be positive (that is, at least one person has the disease)? Suppose now that the blood test yields a positive result. b. What is the probability, under this circumstance, that more than one person has the disease? Now, suppose one of the 500 people is Jones, who knows that he has the disease. c. What does Jones think is the probability that more than one person has the disease? Because the pooled test was positive, the authorities have decided to test each individual separately. The first i -1 of these tests were negative, and the with one—which was on Jones—was positive. d. Given the preceding scenario, what is the probability, as a function of i, that any of the remaining people have the disease?
Solution Summary: The author calculates the probability that the blood test will be positive. Each of 500 soldiers in an army company has a certain disease with probability 1/103.
Each of 500 soldiers in an army company independently has a certain disease with probability
1
10
3
. This disease will show up in a blood test, and to facilitate matters, blood samples from all 500 soldiers are pooled and tested, a. What is the (approximate) probability that the blood test will be positive (that is, at least one person has the disease)? Suppose now that the blood test yields a positive result.
b. What is the probability, under this circumstance, that more than one person has the disease? Now, suppose one of the 500 people is Jones, who knows that he has the disease.
c. What does Jones think is the probability that more than one person has the disease? Because the pooled test was positive, the authorities have decided to test each individual separately. The first i -1 of these tests were negative, and the with one—which was on Jones—was positive.
d. Given the preceding scenario, what is the probability, as a function of i, that any of the remaining people have the disease?
EXAMPLE 6.2
In Example 5.4, we considered the random variables Y₁ (the proportional amount
of gasoline stocked at the beginning of a week) and Y2 (the proportional amount of
gasoline sold during the week). The joint density function of Y₁ and Y2 is given by
3y1, 0 ≤ y2 yı≤ 1,
f(y1, y2) =
0,
elsewhere.
Find the probability density function for U = Y₁ - Y₂, the proportional amount of
gasoline remaining at the end of the week. Use the density function of U to find E(U).
7.20
a
If U has a x² distribution with v df, find E(U) and V (U).
b Using the results of Theorem 7.3, find E(S2) and V (S2) when Y₁, Y2,..., Y, is a random
sample from a normal distribution with mean μ and variance o².
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