There are many different variations of the "least likely" type of question on the GRE, but most of them require you to determine what idea or concept the author would least likely agree with. To answer such questions carefully, you'll have to gauge the tone and attitude that is conveyed in the reading passage, and you'll for sure have to consider all of the answer choices because several of the provided choices may be correct, but only one of them is most correct.

To eliminate answer choices from such "least likely" questions, consider doing the following:

• Eliminate those answer choices which discuss an idea or topic which is explicitly provided as favorable evidence in the reading passage. Very often a fact which is stated in the reading passage is reiterated in one of the answer choices, but don't assume that the direct reference necessarily contradicts the author's opinion. Don't be fooled into picking one of the answer choices just because it references a detail explicitly stated in the reading passage.
• Watch out for generalizations. For example, if in the passage it is written, "The members of the arctic expedition grudgingly weathered the brutal storm for two weeks...", you can't necessarily assume that the members of the expedition are always grumpy -- it just so happened that at one instance, at one time, the members of a group were unhappy with their situation.
• Eliminate those answer choices that are not at all related to the content of the reading passage. For example, if a reading passage is concerned solely about the history of slavery, then for sure you can eliminate any answer choice that, for example, is concerned with post-modernism thought, especially if post-modernism is not mentioned in the passage.

Once you have eliminated those answer choices that you for sure know cannot be the correct answer, you may be left with two (or more) choices which you believe the author would not agree with. In such a case, you'll have to select that choices that is most contrary to the author's opinion. In such a case, again consider key words. For example, if the tone that is conveyed in the reading passage is ambitious and positive, then the answer choice that is most negative and which is contrary to the author's opinion is most likely the correct answer.