Name
Review for Chapter 6 Test
For each of the following, determine:
a) Is this problem asking you find an interval or a sample size
b) If it is an interval, is this problem asking you to use means, proportions, or variance/standard
deviation - Name the interval (z-interval for means, t-interval for means, z-interval for
proportions, or chi square interval for variance or standard deviation)
c) If it is asking for a sample size, are you looking for proportions or means
d) For an interval show how the conditions are met
z-interVal
t-interval
Proportion
Randomly selected
Randomly selected
Randomly selected
11 is
Normally distributed
known
Normally distributed or
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Chi Square interval
Randomly selected
Population is normally
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e) 'Show the computations (check them in the calculato'r ~sing stat, test, and then appropriate
interval)
f) Draw a conclusion
1.
You randomly select and weigh 30 samples of an allergy medication. The sample standard
deviation is 1.2 milligrams. Assuming the weights are normally distributed, construct 99%
confidence intervals for the population variance and standard deviation.
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2.
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In a survey of 1250 US adults, 450 of them said that their favorite sport to watch is baseball.
Construct a 90% confidence interval for the proportion of USadults who say baseball is their
favorite sport to watch. A""'\)rY\e
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_ 3.
You want to estimate the mean price of all the textbooks in the college bookstore.
How many
books must be included in your sample if you want to be 99% confident that the sample mean is
within $5 of the population mean?
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A researcher wishes to estimate the number of household with two cars. How large a sample 'is .
needed in order to be 95% confident that the sample proportion will not differ from the true
proportion by more than 4%7 We don't know the proportion of housenold with two cars from a
previous study.
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S.. A random sample of 32 textbook prices (rounded to the nearest dollar) is taken from a local
college bookstore.
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34
38
45
45
45
45
54
56
65
65
66
67
67
68
74
79
86
87
87
87
88
90
90
94
95
96
98
98
101
110
121
Use a 95% confidence level and find the margin of error for the mean price of all textbooks in
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the bookstore.
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6.
Assume the heights of mean are normally distributed. A random sample of 16 men have a mean
height of 67.5 inches and a standard deviation of 2.8 inches. Construct a 99% confidence
interval for the population standard deviation, cr.
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A manufacturer of golf equipment wishes to estimate the number of left-handed golfers.
a) How large a sample is needed in order to be 98% confident that the sample proportion will
not differ from the true proportion by more than 5%?
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8.
The grade point averages for 10 randomly selected students are listed below. Construct a 90%
confidence interval for the population standard deviation, a. Assume the data are normally
distributed.
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9.
A simple random sample of 100 eighth graders at a large suburban middle school indicated that
83% of them are involved with some type of after-school activity. Find the margin or error for
this sample result if we are to have 90% confidence in the results. What is the confidence
interval?
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10. In a random sample of 20 customers at a local fast food restaurant, the mean waiting time to
order is 95 seconds, and the standard deviation is 21 seconds. Assume the wait times are
normally distributed and construct a 90% confidence interval for the mean wait time of all
customers.
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