GMAT Critical Reasoning, GMAT Verbal
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Critical Reasoning: Strengthen/Weaken – Type 1

We have covered almost all the Critical Reasoning question types on the blog. A few readers had asked for specific posts on the Strengthen/Weaken Type, so the next few posts will cover these two question types in detail. Strengthen/Weaken question types together constitute the maximum number of questions out of the 13-15 Critical Reasoning questions you will encounter on the Verbal section of the GMAT.

Strengthen/Weaken questions are usually broadly based on three types of argument structures:

  • Plan of Action
  • X causes Y
  • Correlation-Causation

We will take up one argument structure at a time and discuss the process to solve each type.

Argument Structure 1: Plan of Action

A lot of Critical Reasoning arguments fall into the plan of action category. What is this category? The argument will be of the type: Do X, Get Y

All of these arguments will be in the form of proposals/recommendations/plans where one action (X) is proposed in expectation of getting a particular outcome.

Whenever you encounter such an argument structure on Strengthen/Weaken you should look for only two types of answer options:

  • options that revolve around the implementation of the plan
  • options that revolve around the side-effects of the plan
Implementation Easy to implement Not implementable
Side-effects No side-effects Side-effects that will affect Y

Let us a take a few GMAT questions to observe this pattern:

Option Type 1: Implementation

Weaken Type
Dutch elm disease, which is caused by the fungus C. ulmi spread by adult scolytid beetles, has already destroyed 70 percent of the elms in Greenwood Forest. Another naturally occurring fungus, P. oblonga, kills larvae of the scolytid beetle. Forest rangers plan to introduce P. oblonga into Greenwood Forest in order to save the remaining mature elms.

Which of the following, if true, would cast the most serious doubt on the plan’s prospects for success?

(A) During the last year, the scolytid beetle population in Greenwood Forest has decreased by 30 percent because of cold-weather conditions.
(B) Dutch elm disease cannot be abated by introducing chemical compounds used to arrest the diseases of many other species of tree.
(C) Introduction of P. oblonga saved elm trees in neighboring Gatemar and Lavemont forests.
(D) For P. oblonga to control scolytid beetles successfully, it must be established in a forest prior to the beetle infestation.
(E) Greenwood Forest has lost many maple trees because of a fungus infection.

The argument clearly follows the Do X, Get Y structure: Introduce P. oblonga to save the remaining mature elms.

For a weaken question an option around implementation will throw up issues with implementation.

Option (D), the correct option does just that — for the plan to work the implementation should have been done at an earlier stage and not now.

For a strengthen question an option around implementation will show that the plan is easily implementable.

Strengthen Type
Which of the following, if true about P. oblonga, provides the strongest evidence that the plan will succeed?

(A) It is spread by a variety of birds that nest in trees that are the home of scolytid beetle larvae.
(B) It has been known to lie dormant within a tree for up to ten years before it begins to reproduce.
(C) It spreads more slowly than C. ulmi, under most climatic conditions.
(D) It does not destroy some commonly found subspecies of scolytid beetles.
(E) It has been known to kill maple trees by destroying their root systems

Option (A), the correct option shows that the plan is easily implementable — it is spread by a variety of birds that nest in trees that are the home of scolytid beetle larvae.

Let us look one more PoA argument that has an option type around implementation.

To reduce the danger to life and property posed by major earthquakes, scientists have been investigating several techniques for giving advance warning of dangerous earthquakes. Since catfish swim erratically before earthquakes, some investigators propose monitoring catfish to predict dangerous earthquakes.

Which of the following, if true, most seriously undermines the usefulness of the proposal?

(A) In Japan, which is subject to frequent earthquakes, the behavior or catfish has long been associated with earthquakes.
(B) Mechanical methods for detecting earthquakes have not been effective.
(C) Tremors lead to the release of hydrogen sulfide gas into the water, thereby causing various fish and shellfish to behave erratically.
(D) Careful construction can reduce the dangers posed by earthquakes.
(E) Even very slight fleeting tremors can cause catfish to swim erratically.

What is the argument? Monitor catfish to predict “dangerous” earthquakes.

It is very important to define the X and Y very precisely as the whole question changes if the word dangerous is removed!

Option (E), the correct option, shows that the plan is not implementable since catfish swim erratically even for the slightest tremor. So while you can monitor catfish you cannot predict whether there will be a dangerous earthquake since catfish will swim erratically even for the smallest tremor, making the plan un-implementable.

Option Type 2: Side effects
The only other way to strengthen/weaken a PoA argument type revolves around the presence or absence of side effects. Let us look at a couple of questions to understand this pattern.

Weaken Type
Some manufacturers of computer software have proposed cutting costs by distributing instruction manuals for their programs on computer disk only, so that computer users can refer to them on a computer screen rather than having to deal with unwieldy printed manuals that are costly for manufacturers to produce.

Which of the following, if true, provides the best reason against adopting the proposal described above?

(A) Most computer users are just as comfortable using instructions on a computer screen as they are using printed manuals.
(B) Although instructions on a computer disk can be printed out cheaply using a computer printer, such printouts are less convenient to use than instructions displayed on a computer screen.
(C) Because they are expensive and inconvenient to copy, printed instruction manuals provide one of the best deterrents against the illegal copying of software, which costs manufacturers enormous profits.
(D) Instructions supplied on a computer disk are more appropriate for business and educational programs than for computer games and other entertainment software.
(E) Instructions supplied on a computer disk can be designed to provide more extensive and more easily utilized cross-references than those provided by printed manuals.

The argument falls into the PoA type:

Distribute instruction manuals on computer disk only to cut costs (or in other words, increase profits).

Option (C) clearly shows the side effect of executing this plan — removing printed copies, will remove the best deterrent against illegal copying resulting in a decrease in profits.

In the Do X, Get Y argument type, what is most important to establish is that the side effect or unintended consequence should result in Y not being achieved. If the option does not show how the side effect will end up compromising Y, the option is incorrect.

Strengthen Type
As part of major renovations to Flowertown’s Main Street train station, consultants to the train company proposed moving the station’s entrance from its current valuable Main Street location to a low-rent adjoining side street and then leasing the high-rent entrance space to retail businesses. In that way, the train company could easily pay for those and all to other proposed renovations without negative impact on its tight budget.

Which of the following, if true, would most strongly support the consultants’ proposal?

(A) More train commuters are employed in business location on Main Street than in businesses located on the adjoining side street.
(B) A reliable survey of Flowertown’s commuters showed that virtually none of them would use the train any less frequently if the station’s entrance were moved.
(C) The high-rent bock of Flowertown’s Main Street includes several buildings whose owners currently seek to replace long-standing tenants lost in recent months.
(D) If the stations entrance were moved the train company would need to begin costly renovations to its Main Street entrance space.
(E) Ridership on Flowertown trains declined only slightly from 1970 to 1985 while other train companies lost large number of commuters.

The argument again follows the PoA pattern: Move the station’s entrance to pay for renovations without negative impact on the tight budget

Clearly, option (B), the correct option is showing how there would no side effect in terms of number of customers using the train station decreasing if the entrance were moved. This is important because the argument mentions that the budget is tight. So if the number of people using the station decreases, the revenue will decrease making the plan financially infeasible. So as you can see this side effect is also linked to its impact on Y.

So whenever you see a plan of action argument type followed by a Strengthen/Weaken question type just use this hack to reach the correct option in the fastest way.

Also, please remember to use this only when the question type is Strengthen/Weaken since you can have PoA argument type followed by an assumption question or any other question type.

In the next post we will take up the second argument type — X causes Y — for discussion.


  1. Pingback: Critical Reasoning: Strengthen-Weaken — Type 3 | The GMAT Blogger

  2. Ankur Sharma says

    HeLLo Tony,

    The link to Correlation-Causation 2 directs to this page. This page, however, seems to be incorrect.
    If this page is indeed incorrect, would You please link Correlation-Causation 2 with the correct page?

    Thank You.


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