A professor using an open source introductory statistics book predicts that 60%

Question

A professor using an open source introductory statistics book predicts that 60% of the students will purchase a hard copy of the book, 25% will print it out from the web, and 15% will read it online. At the end of the semester, he asks his students to complete a survey where they indicate what format of the book they used. of the 126 students, 71 said they bought a hard copy, 30 said they printed it from the web and 25 said they read it online.

a) What is the number of degrees of freedom required for a goodness of fit test?

A. 3

B. 2

C. 127

D. 126

E. 60

F. 59

G. None of the above

b) The P value of the test is 0.3135. What is an appropriate conclusion for the hypothesis test at the 10% significance level?

A. Fail to reject the null hypothesis. The predictions were inaccurate.

B. Fail to reject the null hypothesis. The predictions were accurate.

C. Reject the null hypothesis. The predictions were inaccurate.

D. Reject the null hypothesis. The predictions were accurate.

E. None of the above.

c) how many students did the professor expect to buy the book?

A. 18.9

B. 31.5

C. 127

D. 75.6

E. 71

F. 60

d) Identify the null hypothesis for testing whether the predictions were inaccurate:

A. All formats used by students are equally likely.

B. Most students will buy a hard copy of the book.

C. The distribution of the format of the book used by the students follows the predicted distribution.

D. The distribution of the format of the book used by the students does not follow the predicted distribution.

E. none of the above.

Explanation / Answer

a)

number of degrees of freedom =categories -1=3-1=2

option B is correct

b)

B. Fail to reject the null hypothesis. The predictions were accurate.

c)

expected to buy book=np=126*0.6=75.6

option D

d)

C. The distribution of the format of the book used by the students follows the predicted distribution.

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