During the construction of the Quebec Bridge in 1907, the bridge’s designer, Theodore Cooper, received word that the suspended span being built out from the bridge’s cantilever was deflecting downward by a fraction of an inch (2.54 centimeters). Before he could telegraph to freeze the project, the whole cantilever arm broke off and plunged, along with seven dozen workers, into the St. Lawrence River. It was the worst bridge construction disaster in history. As a direct result of the inquiry that followed, the engineering “rules of thumb” by which thousands of bridges had been built around the world went down with the Quebec Bridge. Twentieth-century bridge engineers would thereafter depend on far more rigorous applications of mathematical analysis.
Which one of the following statements can be properly inferred from the passage?
Bridges built before about 1907 were built without thorough mathematical analysis and, therefore, were unsafe for the public to use.
Cooper’s absence from the Quebec Bridge construction site resulted in the breaking off of the cantilever.
Nineteenth-century bridge engineers relied on their rules of thumb because analytical methods were inadequate to solve their design problems.
Only a more rigorous application of mathematical analysis to the design of the Quebec Bridge could have prevented its collapse.
Prior to 1907 the mathematical analysis incorporated in engineering rules of thumb was insufficient to completely assure the safety of bridges under construction.
Explanation for Question 3
The question asks you to identify the response that can be properly inferred from the passage. The passage indicates that the Quebec Bridge disaster in 1907 and the inquiry that followed caused the engineering “rules of thumb” used in construction of thousands of bridges to be abandoned. Since the Quebec Bridge disaster in 1907 prompted this abandonment, it can be inferred that these were the rules of thumb under which the Quebec Bridge was being built when it collapsed and that these were the rules of thumb used in bridge building before 1907. Further, since the Quebec Bridge collapsed while under construction and the rules of thumb being used were abandoned as a result, it can be inferred that the rules of thumb used in building the Quebec Bridge and bridges prior to 1907 were insufficient to completely assure the safety of bridges under construction. Finally, since the alternative that was adopted in place of the old engineering rules of thumb was to “depend on far more rigorous applications of mathematical analysis,” it can be inferred that the mathematical analysis incorporated in the engineering rules of thumb used prior to 1907 made them insufficient to completely assure the safety of bridges under construction. Thus, (E) is the correct response.
Response (A) is incorrect. (A) asserts that bridges built before about 1907 were unsafe for the public to use because they were built without thorough mathematical analysis. But this conclusion goes far beyond what is established by the passage. The passage gives evidence only about the safety of bridges built before 1907 while they were under construction. It is silent on whether bridges built before about 1907 were safe when open for use by the public. Moreover, the passage indicates that the rules of thumb used in bridge construction before 1907 were abandoned because the use of those rules did not provide adequate assurance of safety for bridges under construction. It does not follow that bridges built using those rules of thumb (those built before about 1907) actually were unsafe, either while under construction or when open for public use.
Response (B) is incorrect in claiming that Cooper’s absence from the construction site caused the breaking off of the cantilever. The passage does not establish that, had Cooper been at the site, he could have successfully intervened to prevent the cantilever from breaking off. By freezing the project, he might have spared lives by stopping work, but there is nothing in the passage to indicate that he necessarily would have prevented the collapse.
Response (C) is incorrect; there is no evidence in the passage about why nineteenth-century bridge engineers relied on their rules of thumb.
Response (D) is also incorrect. While the passage suggests that a more rigorous application of mathematical analysis would have prevented the collapse of the bridge, it offers no evidence that it is the only way the collapse could have been prevented. For example, it might have been prevented had corrective measures been taken in time.
This question was of medium difficulty, based on the number of test takers who answered it correctly when it appeared on the LSAT.