Q2 - Having an efficient, attractive subway

[geverett]

This question gave me a moment for pause. Not always the most encouraging thing at the beginning of the LR section of the LSAT, but a good reminder to never take anything for granted on this test.

Conclusion: The city needs to purchase new subway cars.

Reason why: Efficient, attractive subway is good economic sense, and we should always do what makes good economic sense.

The argument core would look something like this:

Efficient & attractive subway system
makes good economic sense.
City needs to purchase
+ ------------> new subway cars

City should always do what makes
good economic sense

Alright so we know our conclusion and we have our support. We are asked what would make this conclusion logically follow. In other words we need an assumption that is sufficient to make this conclusion follow from the premises stated. So our answer must be something that addresses what is stated in the conclusion:

Prephrase: Alright well I guess our answer needs to link our premise to our conclusion so I need something that says something along the lines of "purchasing new cars is necessary for an efficient, attractive subway system" or something that states that "the cities obligation to always do what makes good economic sense is sufficient to justify purchasing new subway cars."

(A) This answer choice does not link our premise to our conclusion. There is nothing in here about purchasing new subway cars which is what we need. If anything this answer choice just strengthens the first sentence. Interestingly enough if this answer choice replaced our conclusion, and kept the initial premises in tact then you would have a circular argument.
(B) This answer choice addresses "cost effective subway cars . . ." This is out of scope in regards to our conclusion which talks about "new subway cars". New subway cars do not necessarily have to be cost effective subway cars, and cost effective subway cars do not necessarily have to be new subway cars. Get rid of it.
(C) This is probably the most tempting of the answer choices. The reason it doesn't work, however, is because it makes a case for investment in new subway cars making better economic sense than other investment options open to the city. This answer choice brings in a comparison of new subway cars vs. other investment options. There is nothing in the stimulus where the author makes a case for investment in new subway cars vs. other investment options. He only makes a case for new subway cars on the basis of their making good economic sense not better economic sense than other investment options. Get rid of it.
(D) There is no mention of the new subway cars being affordable or not affordable only that the city should purchase new subway cars because the city should always do what makes good economic sense. Technically something could make good economic sense and be either affordable or not affordable. We just don't have enough information in this stimulus to make sense, and so this answer choice classifies as irrelevant. Get rid of it.
(E) This is what we want. It connects "new subway cars" stating that they are required for the city to have a subway system that is efficient and attractive. In other words it directly connect the first premise we listed in our core up above with the language of the conclusion (new subway cars) mentioned in the stimulus. Keep it and move on.

[aileenann]

Your reasoning looks great. Nice job.

[tamwaiman]

This question takes me quite a lot of time although I can recognize the correct answer (E).

This is a sufficient assumption question, and I have difficulty with the logic chain of the first sentence.

Having an efficient, attractive subway makes good econ. sense.

I tend to interpret it as

efficient, attractive subway --> make good econ. sense

However, if so, I cannot cohere with the whole argument.

efficient, attractive subway --> make good econ. sense (1st sentence)
the city should make good econ. sense (3rd sentence)
efficient, attractive subway --> new subway (E)
---------------------------------------------
the city need new subway (2nd sentence)

Did I make a mistaken reversal in 1st sentence?

[irini101]

I totally agree with tamwaiman, I am confused by how to diagram "having an efficient...makes good ...sense"? Does it convey conditional reasoning?

if it conveys conditional reasoning, there's two way to diagram it:

(1) premise: ea--> ges
ges
conclusion: nsc
answer: ea--> nsc
then combining premise & answer would be: ea--> ges
ea--> nsc
but the conclusion does not follows, seems there's something wrong with the flow

(2) premise: ges--> ea
ges
conclusion: nsc
answer: ea--> nsc
then combining premise & answer would be: ges--> ea--> nsc
the conclusion follows and the flow seems right.

But could any one please help and analyze in which way should we diagram the first sentence of the stimulus?

Any thought would be appreciated! Thanks in advance!

[maryadkins]

tamwaiman is right, and irini101, your (1) is right below.

nice job.

[brandonhsi]

I also don't know how to diagram the first premise, and the conclusion. The second premise is (what makes good economic sense) --> (should always do). "Should always" indicates the necessary condition.

My guess for the first premise is (having an efficient subway system) ---> (make good economic sense). After linking two premises, I get (having an efficient subway system) ---> (should always do). Then, I am not sure to continue to get the answer (E).

[ManhattanPrepLSAT1]

I appreciate the concern over conditional logic (especially since this is a Sufficient Assumption question), however, I would not be inclined to use conditional notation on a question like this--it's number 2 in the section, a bit too early for such a formalistic approach.

My approach would be to recognize the connection between terms. We can grasp from the premises that the city should seek an efficient, attractive subway system (EAS). The argument concludes therefore that the city should purchase new subway cars (NC). We could represent this as:

EAS
------
NC

The assumption being: to have an efficient, attractive subway system, the city must purchase new cars (EAS --> NC).

To get deeper in the notation is bit difficult, and even I would struggle with the notation. But so you can see how it works...

The premises establish:

Having an efficient, attractive subway system makes good economic sense (EAS --> GES). We also know, the city should always do what makes good economic sense (GES --> Do it). From these we can infer (EAS --> Do it). That in essence means the city needs an efficient, attractive subway system (EAS). From there, the link to new cars (NC) is pretty straightforward (EAS --> NC).

Hope that helps!