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Quiz 2 - Chapter 8

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
 

1. 

If we want to provide a 95% confidence interval for the mean of a population, the confidence coefficient is
a.
0.485
b.
1.96
c.
0.95
d.
1.645
 

2. 

From a population that is not normally distributed and whose standard deviation is not known, a sample of 20 items is selected to develop an interval estimate for m.
a.
The normal distribution can be used.
b.
The t distribution with 19 degrees of freedom must be used.
c.
The t distribution with 20 degrees of freedom must be used.
d.
The sample size must be increased.
 

3. 

From a population that is normally distributed, a sample of 25 elements is selected and the standard deviation of the sample is computed. For the interval estimation of m, the proper distribution to use is the
a.
normal distribution
b.
t distribution
c.
t distribution with 26 degrees of freedom
d.
t distribution with 24 degrees of freedom
 

4. 

The z value for a 97.8% confidence interval estimation is
a.
2.02
b.
1.96
c.
2.00
d.
2.29
 

5. 

An interval estimate is a range of values used to estimate
a.
the shape of the population's distribution
b.
the sampling distribution
c.
a sample statistic
d.
a population parameter
 
 
Exhibit 8-2
A random sample of 81 automobiles traveling on an interstate showed an average speed of 60 mph and a standard deviation of 13.5 mph. Assume the distribution of speeds of all the cars is normal.
 

6. 

Refer to Exhibit 8-2. The 86.9% confidence interval for m is
a.
46.500 to 73.500
b.
57.735 to 62.625
c.
59.131 to 60.869
d.
50 to 70
 

7. 

A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 4.8. The 95.44% confidence interval for the population mean is
a.
15.2 to 24.8
b.
19.200 to 20.800
c.
19.216 to 20.784
d.
21.2 to 22.8
 

8. 

The sample size needed to provide a margin of error of 2 or less with a .95 probability when the population standard deviation equals 11 is
a.
10
b.
11
c.
116
d.
117
 

9. 

We are interested in conducting a study in order to determine what percentage of voters of a state would vote for the incumbent governor. What is the minimum size sample needed to estimate the population proportion with a margin of error of 0.05 or less at 95% confidence?
a.
200
b.
100
c.
425
d.
385
 

10. 

A population has a mean of 150 and a standard deviation of 30. A random sample of 100 from this population is selected. The sample has a mean of 145 and a standard deviation of 33. The sampling error is
a.
5
b.
50
c.
45
d.
120
 



 
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