# GMAT Data Sufficiency Strategy - Prove Insufficiency

Perhaps no GMAT item is as symbolic of the test as is a Data Sufficiency question.  It is an iconic question format, unique to the GMAT and true to the aims of this specific test: to reward those who show the higher-order reasoning skills that will lead to success in business.

The corporate world is full of “yes men” and “groupthink” – of the kind of inertia that leads companies to think in the same direction without considering alternate points of view.  To combat that, employers and business schools seek those who can see the entire array of possibility, and the GMAT tests for that in many Data Sufficiency problems.  Consider a problem like:

Is the product jkmn = 1?

(1) jk/mn = 1

(2) j, k, m, and n are integers

Considering statement 1 it’s quite easy to get the answer “NO”.  Using 1, 8, 2, and 4, for example, satisfies statement 1?s constraints but clearly gives a product unequal to 1.  So does 1, 20, 5, and 4.  But having just one “NO” should immediately change your focus toward getting the other answer.  A series of nos using similar numbers (1, the product of two integers, and those two integers is the formula we used to create both options thus far) doesn’t do you any good.

You need to either prove that the statement is sufficient in all cases or find the case or two that doesn’t give the same answer, rendering the statement insufficient.  And in either case you need to try different types of numbers.  With that as your guide, you might be persuaded to try nonintegers as at least a few values:  1/2, 2, 1/4, 4 satisfies statement 1, but also provides the product 1 and the answer “YES”.  We can prove the statement insufficient using these not-as-obvious nonintegers, and that’s why having a goal of insufficiency is so helpful: it forces you to try unique numbers.

Statement 2, however, renders our non-integer choices obsolete.  We can use the same integers as before (1, 8, 4, 2) t o get “YES”, but now we need to try harder to get “NO” as the fractions don’t work.  Here, again, the key to unlocking this one may be in our goal: we want the statement to be insufficient!  So we should push the limits of possibility.

Does the statement say that we can’t repeat numbers?

No!  So we can say that j, k, m, and n are 1, 1, 1, and 1, rendering both statement 2 and both statements together insufficient.   A major component of Data Sufficiency is that it rewards you for playing devil’s advocate – for noting the few unique cases in which a likely conclusion is invalid.  By making that your goal, you can ensure that you’re working toward those unique case numbers (like negatives, fractions, primes, 0) that tend to produce different results.

Author :

Veritas Prep is the world’s largest privately-owned GMAT preparation and admissions consulting provider, offering industry-leading programs to help applicants improve their test scores and gain admission to the world’s best graduate schools. Founded in 2002 by graduates of the Yale School of Management, Veritas Prep is now live in more than 90 cities worldwide, as well as interactive online courses  available everywhere. Additionally, Veritas Prep offers industry-leading admissions consulting services for applicants seeking admission to the most competitive business schools, law schools, and medical schools in the world.

1. Complete GMAT RC Questions in less than 1 minute and 50 seconds
3. Take Notes Effectively
4. Collect and Interpret Facts
5. Speed up Summary Creation
6. Remember Information
7. Question the Author

12. Learn to Answer GMAT organization of passage Question
13. Learn to identify the style/tone or attitude of the author

Mastering GMAT Critical Reasoning

After you read F1GMAT’s Mastering GMAT Critical Reasoning Guide, you will learn:

How to overcome flawed thinking in GMAT Critical Reasoning?

How to spot Inconsistencies in Arguments

How to eliminate out of scope answer choices using Necessary and Sufficient Conditions

How to Paraphrase GMAT Critical Reasoning Question

How to Answer Assumption Question Type

How to Answer Conclusion Question Type

How to Answer Inference Question Type

How to Answer Strengthen Question Type

How to Answer Weaken Question Type

How to Answer bold-faced and Summary Question Types

How to Answer Parallel Reasoning Questions

How to Answer the Fill in the Blanks Question

Get F1GMAT's Newsletters (Best in the Industry)

• Ranking Analysis
• Post-MBA Salary Trends
• Post-MBA Job Function & Industry Analysis
• Post-MBA City Review
• MBA Application Essay Tips
• School Specific Essay Tips
• GMAT Preparation Tips