Sentence Correction

lunarpower wrote:

Fractal wrote:D. would have to know a great deal more than they do now about the social and economic

Would D. also be correct as followed:

D. have to know a great deal more than they do now about the social and economic

... or is the addition of "would" necessary?

thx

no -- that's the same tense as "do", creating a sentence that contradicts itself.

the sentence would work with "would" (implying a purely hypothetical consideration); it would also work with "will" in that place (implying a reasonable chance that this will be possible in the future).

lunarpower wrote:

mmslf75 wrote:

mmslf75 wrote:

reachac wrote:To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.

A. have to know a great deal more than now about the social and economic
B. have to know a great deal more than they do now about the social and economical
C. would have to know a great deal more than they do now about the social and economical
D. would have to know a great deal more than they do now about the social and economic
E. would have to know a great deal more than now about the social and economical

OA here is D,

What's wrong with E

Why cannot we say "KNOW A GREAT DEAL MORE THAN NOW " in lieu of "know a great deal more than they do now"

I have read on BTG / MGMAT forum..dont recall where that when the message is conveyed in the former of the sentence
one need not mention again.. so why here in D we mention ??

Also, if I have a sentence
Tom has always eaten more food than Jerry <has>
Tom has always eaten more food than Jerry < < > >
Tom has always eaten more food than jerry <does>

When does one use DOES/DO/DID in latter part of the sentence, given that we have HAVE/HAS/ in former part of the sentence

What do we use here ???

usually, when you omit verbs like that, you're omitting a verb that's in the same tense as the original verb.

for instance, if you wrote
tom has always eaten more food than jerry
...then the IMPLICATION is
tom has always eaten more food than jerry has.
in other words, if the verb is omitted, then you're (usually, from what i've seen) implying that the omitted verb is of the same tense as whatever other verb appears in the construction.

i.e., in your other sentence - Tom has always eaten more food than jerry <does> - you can't omit the "does", since that omission would destroy the second time frame.

--

if you understand the difference between "economic" and "economical", though, then this isn't a problem in the first place (since "economical" is quite incorrect).

great, Ron, but I have different perspective of this point.

in many gmatprep questions , I see gmat prefer to keep "do" in the second half of comparion even when there is no ambuguity. Namely,

I sing better than you do

is prefered to

I sing better than you

This preference happens many time on some gmatprep questions which I do not remember. So the matter is PREFERENCE, a mechanical rule , not the matter of parallelism.

I already posted my idea on manhantan forum, please, Ron, give us your idea on this point. Thank you Ron.

lunarpower wrote: for instance, consider #38 in the OG verbal supplement. in that problem, some choices have "do"; the others don't. however, both versions are fine -- that problem is decided by other issues.
also note that this problem is a counterexample to what you've written above: viz., "than..." and "than do..." are both fine, but the correct answer uses the former.