The Assumption Question is a Critical Reasoning Question Type on the GMAT® that gives test-takers a certain amount of trouble (the most troublesome being the Boldfaced Question Type). Test-takers often say that they have trouble in attaining a certain level of consistency on this question type. In this post we shall look at a standard operating procedure that will help you increase your accuracy level and choose the right option when faced with two seemingly correct options.

EASY
Civil trials often involve great complexities that are beyond the capacities of jurors to understand. As a result, jurors’ decisions in such trials are frequently incorrect. Justice would therefore be better served if judges rather than juries decided the more complex trials.

The argument above depends on which of the following assumptions?

(A) A majority of civil trials involve complexities that jurors are not capable of understanding.
(B) The judges who would decide complex civil trials would be better able to understand the complexities of those trials than jurors are.
(C) The judges who would preside over civil trials would disallow the most complex sorts of evidence from being introduced into those trials.
(D) Jurors’ decisions are frequently incorrect even in those civil trials that do not involve great complexities.
(E) The sole reason in favor of having juries decide civil trials is the supposition that their decisions will almost always be correct.

Jurors cannot understand the complexities involved in civil trials, hence they need to be decided by judges; the assumption is that judges are better at understanding the complexities in civil trials, option (B).

While easy questions can be solved intuitively like the one above can be solved intuitively, difficult questions, like the one below, will have options that are very relevant to the passage but are not the assumption on which the conclusion is based.

MEDIUM
Since 1941 Los Angeles has drawn water from mountain streams that feed into Mono Lake. If water continues to be drawn from the streams at the present rate, in about 30 years the resulting drop in the water level of Mono Lake will trigger a chain reaction ending in the destruction of the ecosystem of the lake.

Which of the following is an assumption on which the prediction is based?

(A) Since 1941 the ecosystem of Mono Lake has changed significantly as a result of a drop in the lake’s water level.
(B) The amount of water that evaporates from Mono Lake has increased annually since at least 1941.
(C) Los Angeles is investigating the availability of a different source of water that could supplement the water it draws from the mountain streams.
(D) Voluntary water conservation will not by itself be sufficient to hold Los Angeles’ water needs to present levels.
(E) Any water flowing into Mono Lake from sources other than the mountain streams will be insufficient to prevent the triggering event from occurring.

Most test-takers vacillate between (A) and (E); the former is a very good trap option. Such options cannot be eliminated intuitively; the only way to get the tough Assumption questions correct is by following the Negation Method.

All Critical Reasoning passages have the following structure:

Premise 1 + Premise 2 = Conclusion/Assertion/Plan of Action

In the Assumption Question Type, one of the premises will be missing, and thus it follows that without this premise this conclusion cannot be valid.

So the best way of eliminating options on Assumption Questions is by checking if the conclusion will hold even if the option is not true.

Since 1941 Los Angeles has drawn water from mountain streams that feed into Mono Lake
+
Missing Premise (Assumption)
=
If water continues to be drawn from the streams at the present rate, in about 30 years the resulting drop in the water level of Mono Lake will trigger a chain reaction ending in the destruction of the ecosystem of the lake (Conclusion/Prediction)

Let us take each option and examine whether the conclusion will be valid, if the option is not true.

(A) even if since 1941 the ecosystem of Mono Lake has not changed significantly as result of a drop in the lake’s water level, it cannot be said that the prediction will fail since it can change in the next 30 years after water level falls below a particular threshold.

(B) even if the amount of water that evaporates from Lake Mono has not increased annually, the prediction will not become invalid since it is based on the rate at which water is being drawn by Los Angeles from Lake Mono

(C) if Los Angeles is not investigating the availability of a different source of water that could supplement the water it draws from the mountain streams, the prediction will definitely be valid

(D) even if voluntary water conservation will by itself be sufficient to hold Los Angeles’ water needs to present levels, the prediction will not fail since it is based on present levels

(E) if any water flowing into Mono Lake from sources other than the mountain streams will be sufficient to prevent the triggering event from occurring, then the prediction will fail!

To get this method right, it is advisable to take questions from the GMAT Official Guide and practice applying it, so that in case you encounter a tough Assumption Question on the GMAT®, you can switch to this strategy to answer the question correctly.

As I have mentioned quite a few times before the GMAT, like test cricket, is all about technique. The ability to consistently apply the negation method accurately when faced with Assumption question is the best example of what I mean by technique.

Do post any queries you might have on a post in the comments section. Also feel free to post Assumption Questions from the OG, which you find tough, in the comments section and we can discuss how to apply negation method.