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2.128 Blue versus red exam study. In a study of how external

clues influence performance, psychology professors at the

University of Alberta and Pennsylvania State University

gave two different forms of a midterm examination to a

large group of introductory psychology students. The ques-

tions on the exam were identical and in the same order, but

one exam was printed on blue paper and the other on red

paper (Teaching Psychology, May 1998). Grading only the

difficult questions on the exam, the researchers found that

scores on the blue exam had a distribution with a mean

of 53% and a standard deviation of 15%, while scores on

the red exam had a distribution with a mean of 39% and

a standard deviation of 12%. (Assume that both distribu-

tions are approximately mound shaped and symmetric.)

a. Give an interpretation of the standard deviation for the

students who took the blue exam.

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b. Give an interpretation of the standard deviation for the

students who took the red exam.oq oli svi

c. Suppose a student is selected at random from the group

of students who participated in the study and the stu-

dent's score on the difficult questions is 20%. Which

exam form is the student more likely to have taken, the

blue or the red exam? Explain. slitness

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