Dirt roads may evoke the bucolic simplicity of another century, but fi

Read the option as X costs twice as much as Y and then look for parallelism. If we had something like

... to maintain dirt roads costs twice as much as to maintain paved roads.

We'd have ended up with a super awkward (but parallel) construction. In its current form, option E reads

... to maintain dirt roads costs twice as much as for paved roads.

I don't understand what's super awkward there to maintain is parallel to to maintain

Just because something is parallel doesn't mean that it is correct. There could be any number of other things wrong with an option in which parallel construction is maintained.

By the way, my example was just to help show that the elements in option E are not parallel.

... to maintain dirt roads costs twice as much as for paved roads.

GMATNinjaTwo
Hi I just watched you GMAT webinar for SC and i must say they are just the best.
I still have a doubt in Option B . Do is a pronoun that refers to something that is plural and so in this context it is referring to The Cost of maintaining the Paved roads where cost is singular. Can you please explain.
Thanks in advance

Do is a pronoun that refers to something that is plural and so in this context it is referring to The Cost of maintaining the Paved roads where cost is singular.

C, D, E - These can be eliminated instantly because of subject verb agreement issue - 'dirt roads' is plural where as 'costs' is singular.

Dirt roads may evoke the bucolic simplicity of another century, but financially strained townships point out that dirt roads cost twice as much as maintaining paved roads.


(A) dirt roads cost twice as much as maintaining paved roads

(B) dirt roads cost twice as much to maintain as paved roads do

(C) maintaining dirt roads costs twice as much as paved roads do

(D) maintaining dirt roads costs twice as much as it does for paved roads

(E) to maintain dirt roads costs twice as much as for paved roads

I don't understand why (C) is incorrect?
maintaining dirt roads costs twice as much as [maintaining] paved roads do [costs]?

This is all about being supremely literal with comparisons, as we'll discuss in this week’s YouTube webinar. And I don't think that anybody really loves comparisons, so… I dunno, try to enjoy this one anyway.


This is literally saying that dirt roads themselves cost more than maintaining paved roads. That doesn’t work: we either need to compare “maintaining dirt roads” to “maintaining paved roads” or we can compare the two types of roads. But (A) makes no sense in its current form.


This sounds pretty good! The key here is that the word “do” can replace a verb phrase – and in this case, “do” replaces “cost… to maintain.” So this is saying that “dirt roads cost twice as much to maintain as paved roads [cost to maintain].” Great, that makes sense. Let’s keep (B).


This is lamentably subtle. Keep in mind that “do” replaces a verb phrase – and “maintaining” is a noun (gerund) in this case, and definitely not a verb. (For more on –ing words, check out this article: https://gmatclub.com/forum/experts-topi ... 39780.html.) So this is literally saying that “maintaining dirt roads costs twice as much as paved roads [cost].” Now we’re comparing the cost of maintaining dirt roads with the cost of paved roads themselves, and that doesn’t makes sense.

Tricky, but definitely wrong. (C) is gone.


The “it” jumps out at me here. If we’re being charitable, I suppose we could accept the idea that “it” refers back to “maintaining”, since “maintaining” is a noun. So we have “maintaining dirt roads costs twice as much as [maintaining] does for paved roads.” Really? I guess that’s not totally illogical, but it’s a muddy mess, and it’s a whole lot less clear than (B). So (D) is out, since (B) is undoubtedly clearer.


I don’t see any reason why we would use the infinitive “to maintain” as a noun here. That’s not something that you’ll see very often in correct answers on the GMAT. I’m not 100% certain that it’s absolutely wrong, but it’s definitely inferior to (B).

Just as importantly, if we’re going to use the infinitive “to maintain” as the subject of the clause, then it’s only going to makes sense if the comparison is parallel. Something like “to maintain dirt roads costs twice as much as to maintain paved roads” would at least be parallel. (E) in its current form doesn’t make any sense, since “to maintain dirt roads” is compared with just the prepositional phrase “for paved roads.”

So (B) is our winner.

(C) maintaining dirt roads costs twice as much as paved roads do

Well, thanQ for the explanation..

in the 3rd option,
Cant we replace "do" with maintaining costs"???
then we can attain parallelism

Formatting issues aside, I've always loved this question as a great example of a comparison error.

When a comparison is drawn on a sentence correction question, two major themes should jump out at you:

1) The two things compared must be compared in equivalent form.

Here, we could compare:

Dirt roads to paved roads
Maintaining dirt roads to maintaining paved roads

But comparing "the cost of maintaining dirt roads" to "paved roads" is incorrect - one is a cost, and the other is a road...they could never be alike!

Make sure that, when a comparison is drawn, you check to ensure that the two items are in equivalent form. I like to envision a balance scale from chemistry class as a mental picture. If I'm weighing a substance in a petri dish I must account for the weight of the dish on the other side of the balance! Similarly, if I'm comparing a cost of one item, I have to make sure I compare it directly to the cost of the other.


2) Comparison idioms should be in the right form.

This one doesn't have a mistake, but you should get in the habit of seeing:

"As Many As" or "As Much As" ---> Equality
"So Many That" or "So Much That" ---> Critical Mass (e.g. "there is so much pollution in the air that we can't go outside")
"More Than" or "Less Than" ---> Inequality

An easy way for the testmakers to write a wrong-but-tricky answer is to criss-cross these idioms (e.g. "As many that" or "More...as")


In this case, the comparisons are all off but one:

A) Dirt roads cost vs. Maintaining paved roads
B) Dirt roads cost vs. paved roads do ("do" takes the place of "cost") ---> CORRECT!
C) Maintaining dirt roads costs vs. paved roads cost
D) Maintaining dirt roads costs vs. it does
E) To maintain dirt roads vs. for paved roads


Only B puts each element in the same form, so B is a correct comparison while the others miss the mark.