In developing an interval estimate if the population standard deviation is unknown
Answers
Answer:
3. In developing an interval estimate, if the population standard deviation is unknown
Then
the sample standard deviation can be used
Answer:
we want to provide a 95% confidence interval for the mean of a population,
the confidence coefficient is
0.485
1.96
0.95
1.645
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3. In developing an interval estimate, if the population standard deviation is unknown
it is impossible to develop an interval estimate
the standard deviation is arrived at using historical data
the sample standard deviation can be used
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4. In general, higher confidence levels provide
wider confidence intervals
narrower confidence intervals
a smaller standard error
unbiased estimates
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5. A random sample of 81 automobiles 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.
(a) If we are interested in determining an interval estimate for μ at 86.9% confidence,
the Z value to use is
1.96
1.31
1.51
2.00
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(b) The standard error of the mean is
13.5
9
2.26
1.5
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(c) If the confidence coefficient is reduced to 0.8, the standard error of the mean
will increase
will decrease
remains unchanged
becomes negative
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(d) The 86.9% confidence interval for μ is
46.5 to 73.5
57.735 to 62.625
59.131 to 60.869
50 to 70
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(e) If the sample size was 20 (other factors remain unchanged), the interval for μ would
not change
become narrower
become wider
become 0
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6. The manager of 7-11 store has taken a random sample of 100 customers.
The average length of time it took these 100 customers to check out was 3 minutes.
It is known that the standard deviation of the checkout time is one minute.
(a) The standard error of the mean equals
0.001
0.01
0.1
1
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(b) The 95% confidence interval for the true average checkout time is
3 to 5
1.36 to 4.64
1.0 to 5.0
1.04 to 4.96
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