Problems w/ LR Question

[maxse]

I got this question wrong, and still dont really understand why the answer is what it is. Perhaps you guys can help.

"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 also 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 seriou need of rehabilitation.
E) Some bridges that werebuilt according to faulty engineering design are not bridges other than suspension bridges.

[Wall]

A!

[Kwertee]

C!

[LS]

From the following info,

"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..."

We know C is obviously correct, but why A is wrong?

[LS]

Oh! I think A may be wrong. Because from the message we cannot deduce A is good.

[Kwertee]

A is not wrong as much is it isn't necessarily true.  It is possible that all suspension bridges were built from 1950-1960, in which case they are all in serious need of rehabilitation.

[LS]

Kwertee
Yes, good point!

[maxse]

wowo guys you are awesome! ITs like a tutoring service here lol. How are you able to pick out the main point like that though. I too picked A for this question. The answer IS C. But I still dont really see why the choice C is more complete than choice A.

[annchris]

A is not wrong as much is it isn't necessarily true.  It is possible that all suspension bridges were built from 1950-1960, in which case they are all in serious need of rehabilitation.

       

Well, choice C is more complete than choice A because, as Kwertee said, choice A is not necessarily true.  As he said ALL suspension bridges may be in need of serious rehab.  Also, consider that NO suspension bridges were ever built were built during the time frame between 1950 and 1960 (and there is nothing in the paragraph which indicates there must have been some built) then there would be none to be in need of serious rehab.

The question asks which MUST be true, so C is a better answer because there is no way to possibly make the statement false from the information given.  The first part of the question says "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."  So, if we know that at least SOME bridges built during this time frame were built according to faulty engineering design, there MUST be some that are in serious need of rehab if ALL bridges built within that time frame are in need of rehab. 

[Kwertee]

A is not wrong as much is it isn't necessarily true.  It is possible that all suspension bridges were built from 1950-1960, in which case they are all in serious need of rehabilitation.

       

Well, choice C is more complete than choice A because, as Kwertee said, choice A is not necessarily true.  As he said ALL suspension bridges may be in need of serious rehab.  Also, consider that NO suspension bridges were ever built were built during the time frame between 1950 and 1960 (and there is nothing in the paragraph which indicates there must have been some built) then there would be none to be in need of serious rehab.

There being none in need of rehab is not inconsistent with choice A, however.  Choice A just says that some (read: at least one) are not in need of rehab.  Some does not mean 'not all'.