Chapter 9 - Examples
1. For the following problems:
a. Determine the null hypothesis
b. Determine the alternative hypothesis
c. Classify the hypothesis test as a two-tailed test, a left-tailed test, or a right-tailed test
2. The World Almanac, 1985, reports that the mean travel time to work in 1980 for all
South Dakota residents was 13 minutes. A transportation official wants to use a sample
of this year's travel times for South Dakota residents to decide whether the mean travel
time to work for all South Dakota residents has changed from the 1980 mean of 13 minutes.
3. The R.R. Bowker Company of New York collects information on the retail prices of books. In 1990 the mean
retail price of all hard cover history books was $35.44. Suppose we want to perform a hypothesis test to
decide whether this year's mean retail price of all hard cover history books has increased over the 1990 mean.
4. As reported by the U.S. Office of Juvenile Justice and Delinquency Prevention, the mean age of all
juveniles held in public custody in 1989 was 16.0 years. The ages of a random sample of juveniles currently
being held in public custody are to be used to decide whether this year's mean age of all juveniles being
held in public custody is less than the 1989 mean of 16.0 years.
5. Determine at the 95 % confidence level:
a. the rejection region
b . non rejection region
c. critical value(s)
d. the significance level
e. identify the test as right-tailed, left tailed or two tailed.
6. The World Almanac, 1985, reports that the mean travel time to work in 1980 for all South Dakota
residents was 13 minutes. A transportation official wants to use a sample of this year's travel times
for South Dakota residents to decide whether the mean travel time to work for all South Dakota residents
has changed from the 1980 mean of 13 minutes.
7. The R.R. Bowker Company of New York collects information on the retail prices of books. In 1990
the mean retail price of all hard cover history books was $35.44. Suppose we want to perform a hypothesis
test to decide whether this year's mean retail price of all hard cover history books has increased over the 1990 mean.
8. As reported by the U.S. Office of Juvenile Justice and Delinquency Prevention, the mean age of all juveniles
held in public custody in 1989 was 16.0 years. The ages of a random sample of juveniles currently being held in
public custody are to be used to decide whether this year's mean age of all juveniles being held in public custody
is less than the 1989 mean of 16.0 years.
9. Suppose we want to perform a large-sample hypothesis test for a population mean, u, with null
hypothesis: Ho: m = m
o
If the hypothesis test is to be performed at the 5% significance level, find the critical value(s) for
α
a. right-tailed test
b. two-tailed test
c. left-tailed test
10. A dog-food manufacturer sells "50-lb" bags of dog food. Suppose you randomly select 75 bags and find that
the mean is 50.11 lb and s = .84 lb. Would you be inclined to believe that the actual mean weight,
m , of all bags of this dog food differs from the
advertised weight of 50 lb? Perform your test at the 5% significance level.
11. Atlas Fishing Line produces a 10 lb test line. Twelve randomly selected spools are subjected
to tensile-strength test. The data give sample mean strength of 9.75 with s = 0.31. Perform the
required hypothesis test at the 5% significance level to decide whether the 10-lb test line is not up to
specifications. Assume the strengths are normally distributed.
