Here we have a strengthen with necessary premise question. Remember that a premise is necessary for a conclusion if the falsity of the premise guarantees or brings about the falsity of the conclusion. First we check to see if the answer choice strengthens the passage, and then, if it does strengthen, we negate the answer choice to see if its negation makes the argument fall apart. If the answer choice does both those things then it is our correct answer.
The conclusion of the argument is: therefore, if railroad is going to be a successful business, then it must concentrate exclusively on one of these two markets.
Why? We are told that train service suffers when a railroad combines commuter and freight services because it does not serve either particularly well when it divides its attention between its freight and commuter customers.
So, what should jump out at you is that we have made a leap from our premise about not servicing commuter and freight customers well, to the railroad being a successful business. We need an answer choice to help connect these two concepts.
Answer choice (C) states: "Unless a railroad serves its customers well, it will not be a successful business."
We can rewrite this: If it is to be a successful business, a railroad must serve its customers well. Contrapositive: If a railroad does not serve its customers well, then it is not a successful business.
Does this answer choice strengthen the argument? Yes. We know that when a train combines commuter and freight service, it does not serve its customers well, which--according to answer choice (C) - makes it not a successful business. Thus, as answer choice (C) states: if a railroad is to be a successful business, it must not combine the two services, i.e. concentrate exclusively on one of these two markets.
Now, does the negation of this answer choice make the argument fall apart? Yes.
Negation: Even if a railroad doesn't serve its customers well, it can be a successful business.
In this case, the railroad no longer necessarily has to concentrate exclusively on one of these two markets, since they can still be a successful business even if they do not serve their customers well.
Thus, answer choice (C) is the correct answer.
Answer choice (D) states: "If a railroad concentrates on commuter service, it will be a successful business."
Does this strengthen the conclusion? Not necessarily. All answer choice (D) says is that if a railroad concentrates on commuter service, it will be a successful business. Concentrating on commuter service does not necessarily mean concentrating EXCLUSIVELY on commuter service. It could mean just putting an emphasis on commuter service. The conclusion advocates concentrating exclusively on one of these two markets.
Furthermore, the negation of this answer choice also doesn't make the argument fall apart.
Negation: Even if a railroad concentrates on commuter service, it can fail as a business. This doesn't mean that concentrating exclusively on one of these services isn't necessary for a railroad to be successful.
Thus, answer choice (D) is not the correct answer.
Hope that clears things up! Please let us know if you have any other questions.
BrendanJune 7, 2017
Hi Naz! Would you mind explaining to me why E is incorrect? I'm trying to figure out why it's wrong but can't seem to get to the bottom of it. It seems like E slightly strengthens the argument by saying the commuters "rarely" want freight service. Depending on whether I negated this properly, it also seems to destroy the conclusion. Please help me identify the flaw in my thought process here. Thank you for your time!
MehranJune 8, 2017
@Brendan (E) definitely seems to strengthen by ruling out the possibility that concentrating exclusively on one of these two markets will turn off potential customers.
The problem with (E) is that it is not necessary to the argument here.
Notice that the negation of (E) actually strengthens the argument even more.
The negation is of (E) is: "Railroad commuters never want freight service as well."
Remember, "rarely" means "sometimes." The logical opposite of "sometime" is "never."
Hope that helps! Please let us know if you have any other questions.
BrendanJune 8, 2017
Thank you!
ReinaDecember 15, 2019
@mehran I'm confused in Naz's explanation why she rewrote answer choice C... can you explain this is a different way please? I think I just need an alternate explanation to understand this question.
