3-2 rule in SC is a way to eliminate obvious wrong answers for a given question. In most of the cases 2 or 3 answer choices are obvious wrong and rest are not. If that is the case, we can outright eliminate the wrong answer choises and focus on rest not so obvious wrong answer choices. Again wrong answer choices can be 2 or 3. for ex lets see the following question:

In the past several years, astronomers have detected more than 80 massive planets, most of them as large or larger than Jupiter, which circle other stars.

A. most of them as large or larger than Jupiter, which circle
B. most of them as large or larger than Jupiter and circling
C. most of them at least as large as Jupiter, circling
D. mostly at least as large as Jupiter, which circle
E. mostly as large or larger than Jupiter, circling

In this example, 3 AC have "most of them" and 2 have "mostly". Considering "most of them" and "mostly", we can eliminate the ACs with "mostly" because "most of them" is better than "mostly". so now we can eliminate 2 ACs, D and E. Now lets focus on A, B, and C. A is wrong because it lacks the correct idiom, which should be "as large as" or larger than". Same with B too. So C should be correct.

Alternatively, we can divide the 5 AC into 2 3 and 2 as per the idiom. if so, the incorrect 3 ACs are A, B and E. If so, we are left with 2 ACs C and D. Between C and D, C is better because the sentence is not talking about the circling of Jupitor rather its about circling of 80 massive planets. so C wins.

So we can use thbis method in any way we feel better. I am sure others have better views.

hope that helps.
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Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

I would say not for all but more than 50% of questoins are of such types.

to be on safe side, if the pattern such as above arrives, 2/3 or 3/2 split can easily be applied.
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Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT