CHS Stats 0200
Chapter 9 Practice
Name: ___________________________________________________ Pd: ______ Date: __________________________
CHAPTER 9 PRACTICE PROBLEMS
Do all work on a separate sheet of paper.
1. A university is interested in evaluating registration processes. Students can register for classes by using either a
telephone registration system or an on-line system that is accessed through the university’s web site. Independent
random samples of 80 students who registered by phone and 60 students who registered online were selected. Of
those who registered by phone, 57 reported that they were satisfied with the registration process. Of those who
registered online, 50 reported that they were satisfied. Based on these data, is it reasonable to conclude that the
proportion who are satisfied is higher for those who register online? Test the appropriate hypothesis using α =
0.05.
2.
Are college students who take a freshman orientation course more or less likely to stay in college than those who
do not take such a course? The article “A Longitudinal Study of the Retention and Academic Performance of
Participants in Freshmen Orientation Courses” reported that 50 of 94 randomly selected students who did not
participate in an orientation course returned for a second year. Of 94 randomly selected students who did take the
orientation course, 56 returned for a second year. Construct and interpret a 95% confidence interval for the
difference in the proportion of returning students who do not take an orientation course and those who do.
3. Do teachers find their work rewarding and satisfying? The article “Work-Related Attitudes” reported the results
of a survey of random samples of 395 elementary school teachers and 266 high school teachers. Of the elementary
school teachers, 224 said that they were very satisfied with their jobs, whereas 126 of the high school teachers
were very satisfied with their work. Based on these data, is it reasonable to conclude that the proportion of very
satisfied teachers is different for elementary school teachers than it is for high school teachers? Test the
appropriate hypothesis using a 0.05 significance level.
4. You have obtained the number of years of education from one random sample of 38 police officers from City
A and the number of years of education from a second random sample of 30 police officers from City B. The
average years of education for the sample from City A is 15 years with a standard deviation of 2 years. The
average years of education for the sample from City B is 14 years with a standard deviation of 2.5 years. Is
there a statistically significant difference between the education levels of police officers in City A and City
B? Test using a 0.05 significance level.
5. Suppose that a school has two buildings - one for girls and the other for boys. Suppose that the principal wants to
know if the pupils of the two buildings are working equally hard, in the sense that they put in equal number of
hours in studies on the average. Statistically speaking, the principal is interested in testing whether the average
number of hours studied by boys is significantly different from the average for girls. A sample of 10 students
from the boy's building and 15 from girl's building are collected and the students are surveyed on the average
number of hours they study daily. The sample mean turns out to be 7.25 hours for boys and 8.5 for girls. Assume
the standard deviation of the boy’s sample is 2.00 hours and for girls 1.75. Test using a significance level of 0.05.
CHS Stats 0200
Chapter 9 Practice
6.
Dr. Jittery is exploring the effects of caffeine on college students. Though caffeine is widely used to defer sleep
and increase the available time per day to perform homework or improve attention in class, too much caffeine
may have negative effects. Dr. Jittery believes fine motor control may be a good measure of the hypothesized
negative effect, and creates a maze-tracing task that will allow her to collect data on how accurately subjects can
move a pointer through the maze. A counter will be kept to measure the number of times the subject bumps the
pointer into a wall of the maze. Her hypothesis is that too much caffeine will affect the accuracy of the maze
tracing. She tests at a level of 0.05 significance before the sample subjects had caffeine and after the test subjects
has six cups of espresso. Is there sufficient evidence to support her claim that caffeine will have an effect on the
number of bumps in the maze-tracing task?
Null Hypothesis: Caffeine will have no effect on the number of bumps
Alternative Hypothesis: Caffeine will have an effect on the number of bumps.
She runs her subjects and the following data is produced:
# of bumps
No Espresso
4
5
0
4
2
4
1
4
# of bumps
6 Cups of Espresso
8
10
9
8
8
11
10
9
7. Using the data in problem #3, construct and interpret a 95% confidence interval for the difference in the
proportion of returning students who do not take an orientation course and those who do.
8. Using the data in problem #4, construct and interpret the appropriate confidence interval estimate of the difference
between the averages.
9. Using the data in problem #5, construct and interpret the appropriate confidence interval estimate of the difference
between the averages.
10. Using the data in problem #6, construct and interpret the appropriate confidence interval estimate of the mean
difference between no caffeine and six cups of espresso.