by JonathanSchneider Sun Dec 07, 2008 12:58 pm
Notice first of all that in question 8 we are dealing with the same subject: "students." As a result, we only need the word "did" to make the proper comparison.
I suppose your re-phrase for #7 is okay, but I wouldn't go with it, only because it sounds a little wonky to me. I don't think you'd ever have to choose between those two versions. In general, you are somewhat free as to where the "do" verb goes in the second part of the sentence.
Consider:
I ate more cookies than she did.
I ate more cookies than did she.
The second is still fine, but it sounds a bit weird, as you indicated.
Now consider:
The American students are more cookies than the foreign students did.
The American students ate more cookies than did the foreign students.
In this case I actually prefer the latter option, where the "did" comes first. Again, both are correct. But why the change in preference? I think it's just because we have a longer comparative body ("the foreign students," as opposed to just "she"). As a result, placing the "did" first more easily highlights the comparison.
Again, I doubt you'll ever see both choices on one SC question on the GMAT. But I hope the above description helps you to think it through a bit : )