Official Solution:
Electrician Magazine surveyed 1,000 electricians who took an advanced certification exam. Of these 1,000 candidates 500 passed the exam and 500 failed. The magazine asked the electricians how many hours they had studied for the exam. It was found that those who passed had studied on average 50 hours, and those who failed had studied on average 20 hours. The magazine concluded that the more hours one studies, the more likely he is to pass.
Which of the following, if true, would most strengthen the conclusion of the magazine?
A. Some of the electricians in the survey actually studied more than 100 hours.
B. Many of those surveyed thought the exam was unnecessary and did not reflect on their ability as electricians.
C. The electricians in the survey all took the exam shortly after reaching five years of experience as an electrician.
D. Many of the electricians who passed had completed a course in electronics covering some of the topics also included in the syllabus of the certification exam.
E. Majority of the electricians who failed had college degrees in a variety of fields not related to electrical subjects.
A
correlation is observed in the survey between the number of study hours and passing the exam. From this correlation it was concluded that a high number of study hours results in passing the exam. A strengthening statement would eliminate another factor that might affect the outcome (whereas a weakening statement would propose an alternative factor that might have affected the outcome).
A. Some of the candidates might have studied more than 100 hours but that information does not help establish an alternative factor that might result in passing the exam. (Note: This statement nonetheless could be a weakening statement if it were mentioned that some candidates WHO FAILED studied more than 100 hours, but in any case such a statement could not be a strengthening statement.)
B. The opinion of the candidates have no role in the argument and hence irrelevant.
C. CORRECT. This option rules out an alternative factor that might result in passing the exam, viz. having more experience. It may so be the case that the more experience one has, the more knowledge he gains in the subject and therefore the less he needs to study for the exam for an equivalent score. Therefore another factor other than studying could have played a role in the difference in the results. Option C confirms that such a difference does not exist and all test takers have equivalent experience. Option C makes both the groups (passed and failed) comparable and thus supports the conclusion that studying for more hours (and not that having more experience) is the reason for passing the exam.
D. This statement is a weakening statement since it proposes an alternative factor that might have contributed to passing the exam. If the candidates who passed gained extra knowledge from some other course that might have helped them pass the exam, then studying more hours is not attributed to passing the certification exam.
E. Like statement D, this statement is also a weakening statement since it proposes an alternative factor that might have contributed to failing the exam. If the candidates who failed were at a disadvantage because they lacked the knowledge of electrical theories gained from degree courses, then studying fewer hours is not attributed to failing the certification exam.
Answer: C
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