#### Chapter 7 Review

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Chapter 7 Review

Chapter 7 Review
• In a study if 200 accidents that required
treatment in an emergency room, 80 occurred
at work. Find the 90% confidence interval of
the true proportion of accidents that occurred
at work.
0.343 < 𝑝 < 0.531
Emergency Room Accidents
Use the data below is the length (min) of a
random selection of popular animated films.
Use the data to estimate the population
variance (standard deviation) in length of
children’s animated films with 99% confidence.
93 83 76 92 77
81 78 75 78 76 100
28.6 < 𝜎 2 < 334.2
5.3 < 𝜎 < 18.3
Length of Children’s Animated Films
• A random sample of 49 shopper showed that
they spend an average of $23.45 per visit at
the Saturday Mornings Bookstore. The
standard deviation of the population is $2.80.
Find a point estimate of the population mean.
Find the 90% confidence interval of the true
mean.
$23.45
$22.79 < 𝜇 < $24.11
Shopping Survey
• A researcher wishes to estimate within $25
the average cost of postage a community
college spends in one year. If she wishes to be
90% confident, how large of a sample would
be necessary if the population standard
deviation is $80.
28
Spending for Postage
• For a certain urban area, in a sample of 5
months, on average 28 mail carriers were
bitten by dogs each month. The standard
deviation of the sample was 3. Find the 90%
confidence interval of the true mean number
of mail carriers who are bitten by dogs each
month. Assume the variable is normally
distributed.
25 < 𝜇 < 31
Dog Bites Postal Worker
• A federal report stated that 88% of children
under the age of 18 were covered by health
insurance in 2000. How large a sample is
needed to estimate the true proportion of
covered children with 90% confidence with a
confidence interval 0.05 wide.
460
Health Insurance Coverage for
Children