A professor using an open source introductory statistics book predicts that 60%
ID: 3363980 • Letter: A
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 completea survey where they indicate what format of the book they used. Of the 126 students, 71 said they bought a hard copy of the book, 30 said they printed it out from the web, and 25 said they read it online.
(a) Identify the null hypothesis for testing whether the predictions were inaccurate:
A. All formats used by students are equally likely.
B. The distribution of the format of the book used by the students follows the predicted distribution.
C. Most students will buy a hard copy of the book.
D. The distribution of the format of the book used by the students does not follow the predicted distribution.
E. None of the above.
(b) What is the contribution to the chi-square statistic from the students who read online?
A. 0.071
B. 0.3135
C. 0.28
D. 1.97
E. 2.32
(c) How many students did the professor expect to buy the book?
A. 31.5
B. 127
C. 75.6
D. 18.9
E. 71
F. 60
(d) What is the number of degrees of freedom required for a goodness of fit test?
A. 126
B. 2
C. 3
D. 59
E. 60
F. 127
G. None of the above.
Explanation / Answer
Ans:
Expected counts will be 0.6*126=75.6,0.25*126=31.5,0.15*126=18.9 for hard copy,printed and online respectively.
a)Option B is correct.
The distribution of the format of the book used by the students follows the predicted distribution.(0.6,0.25,0.15)
b)Chi square for who read>1.97
Option D is correct.
c)
Expected number of hard copies buy=126*0.6=75.6
Option C is correct.
d)Number of categories=3
Degree of freedom=3-1=2
option B is correct.
Observed(O) Expected(E) (O-E)^2/E hard copy 71 75.6 0.280 printed web 30 31.5 0.071 online 25 18.9 1.969 Total= 126 126 2.320Related Questions
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