13. Workers Distractions A recent study showed that
the modern working person experiences an average of
2.1 hours per day of distractions (phone calls, e-mails,
impromptu visits, etc.). A random sample of 50 workers
for a large corporation found that these workers were
distracted an average of 1.8 hours per day and the
population standard deviation was 20 minutes. Estimate
the true mean population distraction time with 90%
confidence, and compare your answer to the results of
the study.
Source: Time Almanac.
14. Golf Averages A study of 35 golfers showed that their
average score on a particular course was 92. The
standard deviation of the population is 5.
a. Find the best point estimate of the mean.
b. Find the 95% confidence interval of the mean score
for all golfers.
c. Find the 95% confidence interval of the mean score
if a sample of 60 golfers is used instead of a sample
of 35.
d. Which interval is smaller? Explain why.
17. Television Viewing A study of 415 kindergarten students
showed that they have seen on average 5000 hours of
television. If the sample standard deviation of the
population is 900, find the 95% confidence level of the
mean for all students. If a parent claimed that his children
watched 4000 hours, would the claim be believable?
18. Day Care Tuition A random sample of 50 four-year-olds
attending day care centers provided a yearly tuition
average of $3987 and the population standard deviation
of $630. Find the 90% confidence interval of the true
mean. If a day care center were starting up and wanted to
keep tuition low, what would be a reasonable amount to
charge?
19. Hospital Noise Levels Noise levels at various area
urban hospitals were measured in decibels. The mean
of the noise levels in 84 corridors was 61.2 decibels,
and the standard deviation of the population was 7.9.
Find the 95% confidence interval of the true mean.
Source: M. Bayo, A. Garcia, and A. Garcia, Noise Levels in an Urban
Hospital and Workers Subjective Responses, Archives of Environmental
Health 50, no. 3, p. 249 (MayJune 1995). Reprinted with permission of
the Helen Dwight Reid Educational Foundation. Published by Heldref
Publications, 1319 Eighteenth St. N.W., Washington, D.C. 20036-1802.
Copyright 1995.
20. Length of Growing Seasons The growing seasons for
a random sample of 35 U.S. cities were recorded,
yielding a sample mean of 190.7 days and the population
standard deviation of 54.2 days. Estimate the true mean
population of the growing season with 95% confidence
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