Assuming that the speeds are approximately normally distributed, how many degrees of freedom will
there be in the appropriate t -test used to determine which type of tennis ball travels faster?
a. 6
b. 7
c. 16
d. 15
e. 14
Two statistics teachers want to compare their teaching methods. They decide to give the same final
exam and use the scores on the exam as a basis for comparison. They decide that the value of interest
to them will be the proportion of students in each class who score above 80% on the final. One class
has 32 students and one has 27 students. Which of the following would be the most appropriate test
for this situation?
a. Two proportion z -test
b. Two-sample t -test
c. Chi-square goodness-of-fit test
d. One-sample z -test
e. Chi-square test for independence
Free-Response
A large high school has been waging a campaign against drug use, particularly marijuana. Before the
campaign began in 2004, a random sample of 100 students from the junior and senior classes found
27 who admitted to using marijuana (we understand that some students who used marijuana would be
reluctant to admit it on a survey). To assess the success of their program, in early 2007 they surveyed
a random sample of 175 juniors and seniors and 30 responded that they have used marijuana. Is this
good evidence that the use of marijuana has been reduced at the school?
- Twenty-six pairs of identical twins are enrolled in a study to determine the impact of training on
ability to memorize a string of letters. Two programs (A and B) are being studied. One member of
each pair is randomly assigned to one of the two groups and the other twin goes into the other group.
Each group undergoes the appropriate training program, and then the scores for pairs of twins are