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Chapter 9: Estimation Using a Single Sample
Name ___________________________
1. Briefly define the following terms in your own words:
a) Confidence interval
b) The confidence level associated with a confidence interval
2. Under what conditions is the z confidence interval an appropriate way to estimate a
population mean?
3. Suppose that a newspaper conducts a survey of a random sample of 120 registered
voters in order to predict the winner of a local election. The Republican candidate
was favored by 62 of the respondents.
a) Construct and interpret a 99% CI for the true proportion of voters who prefer the
Republican candidate.
b) If a candidate needs a simple majority of the votes to win the election, can the
Republican candidate be confident of victory? Justify your response with an
appropriate statistical argument.
Chapter 9 Test, Form B
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4. Reading comprehension is arguably the single most important skill a student
possesses. To assess the current levels of reading comprehension in 3rd grade, 25
students were randomly selected from school district class lists and given a reading
comprehension test. The distribution of their scores was approximately normal with a
mean of 180 and a standard deviation of 20.12. Construct a 99% confidence interval
for m , the population mean.
5. In a very large school district student records have been kept in three distinct data
bases, one each for elementary, middle, and high school. Because of this, data entry
errors tend to be compounded as students move through the grades. The district now
has a new data base and wishes to fix the original data entry errors. To allocate
enough secretarial time to this task, an estimate of the proportion of records that
contain errors must be made. Initial estimates are that there are fixable errors in about
15% of the records. Based on the 15% assumption, compute the sample size
required to estimate the true proportion of records with errors to within .025 with
95% confidence.
Chapter 9 Test, Form B
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6. Many national parks, wildlife refuges, and wilderness areas lie directly below
designated military air space. This raises issues of whether wildlife and, for example,
loud jet noises are compatible. In an effort to evaluate the effects of low-altitude jetnoise, researchers simulated these noises for captive desert mule deer. Three minutes
after the loud noises were played, the heart rates (beats per minute) of these animals
was measured, with the following results:
55.9, 51.1, 57.5, 65.5, 68.4, 64.9, 63.1, 55.3, 63.3
Assume that it is reasonable to think that these deer can be regarded as a random
sample of desert mule deer.
a) Calculate and interpret a 95% confidence interval for the mean heart rate 3 minutes
after loud jet noises.
b) The mean heart rate for desert mule deer is about 51.2 beats per minute. Based on the
confidence interval in part (a), do you think that the loud jet noise has some lingering
effect on the heart rate of desert mule deer? Explain
Chapter 9 Test, Form B
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