13. Coal: Automatic Loader Coal is carried from a mine in West Virginia to a power plant in New York in hopper cars on a long train. The automatic hopper car loader is set to put 75 tons of coal into each car. The actual weights of coal loaded into each car are normally distributed, with mean u = 75 tons 0.8 ton. and standard deviation o = (a) What is the probability that one car chosen at random will have less than 74.5 tons of coal?

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Section 6.5
The Central Limit Theorem
329
(b) What is the probability that 20 cars chosen at random will have a mean
load weight x of less than 74.5 tons of coal?
(c) Interpretation Suppose the weight of coal in one car was less than
74.5 tons. Would that fact make you suspect that the loader had slipped
out of adjustment? Suppose the weight of coal in 20 cars selected at ran-
dom had an average x of less than 74.5 tons. Would that fact make you
suspect that the loader had slipped out of adjustment? Why?
Vital Statistics: Heights of Men The heights of 18-year-old men are ap-
proximately normally distributed, with mean 68 inches and standard devia-
tion 3 inches (based on information from Statistical Abstract of the United
States, 112th edition).
(a) What is the probability that an 18-year-old man selected at random is
between 67 and 69 inches tall?
(b) If a random sample of nine 18-year-old men is selected, what is the
probability that the mean height x is between 67 and 69 inches?
(c) Interpretation Compare your answers to parts (a) and (b). Is the prob-
ability in part (b) much higher? Why would you expect this?
Medical: Blood Glucose Let x be a random variable that represents the level
of glucose in the blood (milligrams per deciliter of blood) after a 12-hour fast.
Assume that for people under 50 years old, x has a distribution that is approx-
imately normal, with mean u
(based on information from Diagnostic Tests with Nursing Applications,
edited by S. Loeb, Springhouse). A test result x < 40 is an indication of
severe excess insulin, and medication is usually prescribed.
(a) What is the probability that, on a single test, x < 40?
(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? Hint: See
Theorem 6.1. What is the probability that x < 40?
(c) Repeat part (b) for n
(d) Repeat part (b) for n
(e) Interpretation Compare your answers to parts (a), (b), (c), and (d). Did
the probabilities decrease as n increased? Explain what this might imply
if you were a doctor or a nurse. If a patient had a test result of x < 40
based on five tests, explain why either you are looking at an extremely
rare event or (more likely) the person has a case of excess insulin.
85 and estimated standard deviation o =
25
= 3 tests taken a week apart.
5 tests taken a week apart.
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 u
7500 and
estimated standard deviation o =
1750 (see reference in Problem 15). A test
result of x < 3500 is an indication of leukopenia. This indicates bone mar-
row 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 I < 3500?
(c) Repeat part (b) for n = 3 tests taken a week apart.
(d) Interpretation Compare your answers to parts (a), (b), and (c). How did
Transcribed Image Text:Section 6.5 The Central Limit Theorem 329 (b) What is the probability that 20 cars chosen at random will have a mean load weight x of less than 74.5 tons of coal? (c) Interpretation Suppose the weight of coal in one car was less than 74.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment? Suppose the weight of coal in 20 cars selected at ran- dom had an average x of less than 74.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment? Why? Vital Statistics: Heights of Men The heights of 18-year-old men are ap- proximately normally distributed, with mean 68 inches and standard devia- tion 3 inches (based on information from Statistical Abstract of the United States, 112th edition). (a) What is the probability that an 18-year-old man selected at random is between 67 and 69 inches tall? (b) If a random sample of nine 18-year-old men is selected, what is the probability that the mean height x is between 67 and 69 inches? (c) Interpretation Compare your answers to parts (a) and (b). Is the prob- ability in part (b) much higher? Why would you expect this? Medical: Blood Glucose Let x be a random variable that represents the level of glucose in the blood (milligrams per deciliter of blood) after a 12-hour fast. Assume that for people under 50 years old, x has a distribution that is approx- imately normal, with mean u (based on information from Diagnostic Tests with Nursing Applications, edited by S. Loeb, Springhouse). A test result x < 40 is an indication of severe excess insulin, and medication is usually prescribed. (a) What is the probability that, on a single test, x < 40? (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? Hint: See Theorem 6.1. What is the probability that x < 40? (c) Repeat part (b) for n (d) Repeat part (b) for n (e) Interpretation Compare your answers to parts (a), (b), (c), and (d). Did the probabilities decrease as n increased? Explain what this might imply if you were a doctor or a nurse. If a patient had a test result of x < 40 based on five tests, explain why either you are looking at an extremely rare event or (more likely) the person has a case of excess insulin. 85 and estimated standard deviation o = 25 = 3 tests taken a week apart. 5 tests taken a week apart. 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 u 7500 and estimated standard deviation o = 1750 (see reference in Problem 15). A test result of x < 3500 is an indication of leukopenia. This indicates bone mar- row 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 I < 3500? (c) Repeat part (b) for n = 3 tests taken a week apart. (d) Interpretation Compare your answers to parts (a), (b), and (c). How did
AND SAMPLING DISTRIBUTIONS
6.
Basic Computation: Central Limit Theorem Suppose x has a distribution
with a mean of 20 and a standard deviation of 3. Random samples of size
36 are drawn.
n =
(a) Describe the x distribution and compute the mean and standard deviation
of the distribution.
(b) Find the z value corresponding to x =
(c) Find P(I < 19).
(d) Interpretation Would it be unusual for a random sample of size 36 from
the x distribution to have a sample mean less than 19? Explain.
19.
7.| Statistical Literacy
(a) If we have a distribution of x values that is more or less mound-shaped
and somewhat symmetric, what is the sample size needed to claim that
the distribution of sample means x from random samples of that size is
approximately normal?
(b) If the original distribution of x values is known to be normal, do we need to
make any restriction about sample size in order to claim that the distribution
of sample means x taken from random samples of a given size is normal?
8.| Critical Thinking Suppose x has a distribution with
(a) If random samples of size n = 16 are selected, can we say anything about
the x distribution of sample means?
(b) If the original x distribution is normal, can we say anything about the x
distribution of random samples of size 16? Find P(68 <S 73).
72 and o = 8.
d
9.| Critical Thinking Consider two ī distributions corresponding to the same x
distribution. The first x distribution is based on samples of size n =
the second is based on samples of size n =
smaller standard error? Explain.
100 and
in
225. Which x distribution has the
10.
Critical Thinking Consider an x distribution with standard deviation o =
(a) If specifications for a research project require the standard error of the
corresponding x distribution to be 2, how large does the sample size need
12.
to be?
(b) If specifications for a research project require the standard error of the
corresponding x distribution to be 1, how large does the sample size need
to be?
11.| Critical Thinking Suppose x has a distribution with u = 15 and o = 14.
(a) If a random sample of size n = 49 is drawn, find u, Oz,
P(15 <ī< 17).
(b) If a random sample of sizen =
P(15 <i< 17).
(c) Why should you expect the probability of part (b) to be higher than that
of part (a)? Hint: Consider the standard deviations in parts (a) and (b).
and
64 is drawn, find µ¡, 07, and
12.
5. Consider two
Critical Thinking Suppose an x distribution has mean u
corresponding r distributions, the first based on samples of size n = 49 and
the second based on samples of size n =
(a) What is the value of the mean of each of the two x distributions?
(b) For which I distribution is P(x > 6) smaller? Explain.
(c) For which distribution is P(4 < x < 6) greater? Explain.
81.
13.| Coal: Automatic Loader Coal is carried from a mine in West Virginia to a
power plant in New York in hopper cars on a long train. The automatic hopper
car loader is set to put 75 tons of coal into each car. The actual weights of
coal loaded into each car are normally distributed, with mean u
0.8 ton.
75 tons
and standard deviation o =
(a) What is the probability that one car chosen at random will have less than
74.5 tons of coal?
gage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-208
Transcribed Image Text:AND SAMPLING DISTRIBUTIONS 6. Basic Computation: Central Limit Theorem Suppose x has a distribution with a mean of 20 and a standard deviation of 3. Random samples of size 36 are drawn. n = (a) Describe the x distribution and compute the mean and standard deviation of the distribution. (b) Find the z value corresponding to x = (c) Find P(I < 19). (d) Interpretation Would it be unusual for a random sample of size 36 from the x distribution to have a sample mean less than 19? Explain. 19. 7.| Statistical Literacy (a) If we have a distribution of x values that is more or less mound-shaped and somewhat symmetric, what is the sample size needed to claim that the distribution of sample means x from random samples of that size is approximately normal? (b) If the original distribution of x values is known to be normal, do we need to make any restriction about sample size in order to claim that the distribution of sample means x taken from random samples of a given size is normal? 8.| Critical Thinking Suppose x has a distribution with (a) If random samples of size n = 16 are selected, can we say anything about the x distribution of sample means? (b) If the original x distribution is normal, can we say anything about the x distribution of random samples of size 16? Find P(68 <S 73). 72 and o = 8. d 9.| Critical Thinking Consider two ī distributions corresponding to the same x distribution. The first x distribution is based on samples of size n = the second is based on samples of size n = smaller standard error? Explain. 100 and in 225. Which x distribution has the 10. Critical Thinking Consider an x distribution with standard deviation o = (a) If specifications for a research project require the standard error of the corresponding x distribution to be 2, how large does the sample size need 12. to be? (b) If specifications for a research project require the standard error of the corresponding x distribution to be 1, how large does the sample size need to be? 11.| Critical Thinking Suppose x has a distribution with u = 15 and o = 14. (a) If a random sample of size n = 49 is drawn, find u, Oz, P(15 <ī< 17). (b) If a random sample of sizen = P(15 <i< 17). (c) Why should you expect the probability of part (b) to be higher than that of part (a)? Hint: Consider the standard deviations in parts (a) and (b). and 64 is drawn, find µ¡, 07, and 12. 5. Consider two Critical Thinking Suppose an x distribution has mean u corresponding r distributions, the first based on samples of size n = 49 and the second based on samples of size n = (a) What is the value of the mean of each of the two x distributions? (b) For which I distribution is P(x > 6) smaller? Explain. (c) For which distribution is P(4 < x < 6) greater? Explain. 81. 13.| Coal: Automatic Loader Coal is carried from a mine in West Virginia to a power plant in New York in hopper cars on a long train. The automatic hopper car loader is set to put 75 tons of coal into each car. The actual weights of coal loaded into each car are normally distributed, with mean u 0.8 ton. 75 tons and standard deviation o = (a) What is the probability that one car chosen at random will have less than 74.5 tons of coal? gage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-208
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