The answer is definitely (D) here.
The biggest issue in this question is the (very cleverly disguised) idiom "as many... as". We use the phrase "as many... as" pretty frequently in normal language:
- Chuck eats three times as many burritos as Mike. --> no problem, right?
- Chuck eats more than three times as many burritos as Mike. --> still no problem, right?
Both of these are acceptable, it's just that they're saying slightly different things. But you wouldn't say either of these:
- Chuck eats three times as many burritos than Mike.
- Chuck eats more than three times as many burritos than Mike.
You could say "as many... as" or "more than" -- but "as many... than" is simply wrong. The error in (A), (B), and (C) is exactly the same as in these last two examples. It's just that the construction is more complicated, so it's harder to spot the error. For example, here's answer choice (C):
Quote:
more than three times as many independent institutions of higher education charge tuition and fees of under $8,000 a year than charge over $16,000
There are a ton of words separating "as many" from "than" -- and that makes it really, really hard to see the mistake. And yes, this is a nasty little trick that you're likely to see in other GMAT SC questions.
Anyway, that leaves us with (D) and (E). As several people have mentioned, there's a parallelism issue in (E), but to be fair, it's really subtle. Here are (D) and (E) again, with a few words stripped out to make it easier to see what's happening:
(D) "... three times as many institutions charge tuition and fees of under $8,000 a year as charge over $16,000."
(E) "... three times as many institutions charge tuition and fees of under $8,000 a year as those charging over $16,000."
The parallelism is much, much clearer in (D): "three times as many institutions do X as do Y." In (E), we're basically saying "three times as many institutions do X as institutions doing Y."
But to be fair: man, this question is tough, and I can introduce you to a whole bunch of people who missed this on their practice tests... and still scored in the mid-700s on the real thing just a few weeks later.
I understand the parallelism argument for choosing D, however, isn't it correct to use those since you are referring to a different group of colleges? In other words, it is a new copy of the same object (in this case group), since the same college can't be charging different tuition. I would appreciate the clarification.