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CAT Critical Reasoning Practice question with Solution 86

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?

[A]. Bridges built before about 1907 were built without thorough mathematical analysis and, therefore, were unsafe for the public to use.
[B]. Cooper's absence from the Quebec Bridge construction site resulted in the breaking off of the cantilever.
[C]. Nineteenth-century bridge engineers relied on their rules of thumb because analytical methods were inadequate to solve their design problems.
[D]. Only a more rigorous application of mathematical analysis to the design of the Quebec Bridge could have prevented its collapse.
[E]. Prior to 1907 the mathematical analysis incorporated in engineering rules of thumb was insufficient to completely assure the safety of bridges under construction.
Answer: E

We’ve got a tragic story: Theodore Cooper, designer of the Quebec Bridge, receives word that there’s danger on the construction site; he telegraphs immediately, but it’s too late, and 84 workers plunge to their death. They didn’t die completely in vain, though; as a result of their misfortune, the process of bridge construction was altered. Whereas engineering “rules of thumb” had been used in the past, they were now abandoned in favor of “rigorous applications of mathematical analysis.” (E) is inferable: Before the Quebec tragedy in 1907, bridge builders had been accustomed to relying on “engineering rules of thumb” (and thus relying on whatever level of mathematical analysis was incorporated in those rules); as the 1907 disaster showed, these rules didn’t ensure complete safety. That’s all (E) says.

(A) is too broad; the Quebec Bridge was unsafe at one period of its construction, but for all we know, plenty of pre-20th century bridges were completely safe for public use, despite their engineers’ reliance on non-rigorous “rules of thumb.”

(B) We’re never told that Cooper’s absence from the site led to the disaster; we don’t know that he would have made a difference if he had been on site. The stimulus blames the then customary lack of rigorous mathematical analysis for the disaster.

(C) We’re never told why 19th century engineers relied on rules of thumb. Maybe their analytical methods were inadequate. On the other hand, maybe it was a matter of timesaving or cost-cutting.

(D) is too strong; we don’t know that more rigorous application of mathematical analysis was the only thing that would have prevented the disaster. Maybe a wholly different bridge design, to take one example, could also have done the job.

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