noboru wrote:
All bridges built from 1950 to 1960 are in serious need of rehabilitation. Some bridges constructed in this period, however, were built according to faulty engineering design. That is the bad news. The good news is that at least some bridges in serious need of rehabilitation are not suspension bridges, since no suspension bridges are among the bridges that were built according to faulty engineering design.
If the statements above are true, then, on the basis of those statements, which one of the following must be true?
(A) Some suspension bridges are not in serious need of rehabilitation.
(B) Some suspension bridges are in serious need of rehabilitation.
(C) Some bridges that were built according to faulty engineering design are in serious need of rehabilitation.
(D) Some bridges built from 1950 to 1960 are not in serious need of rehabilitation.
(E) Some bridges that were built according to faulty engineering design are not bridges other than suspension bridges.
Apply the NEGATION TEST.
When the correct answer is negated, the passage will be contradicted.
Note:
The opposite of SOME X is NO X.
C, negated:
No bridges that were built according to faulty engineering design are in serious need of rehabilitation.
This negation contradicts the following information in the passage:
All bridges built from 1950 to 1960 are in serious need of rehabilitation.
Some bridges constructed in this period were built according to faulty engineering design.Since the negation of C contradicts the passage, C is a valid INFERENCE: a statement that MUST BE TRUE, given the information in the passage.
B, negated:
No suspension bridges are in serious need of rehabilitation.Since the passage states that
at least some bridges in serious need of rehabilitation are not suspension bridges, it is possible that ALL bridges in need of rehabilitation are not suspension.
In other words, it is possible that NO suspension bridges are in need of rehabilitation.
Since the negation of B does not contradict the passage, B is NOT a valid inference.
Eliminate B.
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