The data sufficiency GMAT section is known to cause a lot of confusion among test takers. For most students, GMAT Data Sufficiency (DS) is an entirely new type of math question that is unlike any they’ve encountered on prior exams. For those who are less quant inclined, it’s the hardest part of the GMAT.
In this beginner’s guide, I’ll teach you how to do well on this unique question type and review a few data sufficiency tricks in the process. Also, we’ll go over a few tips on how to solve DS questions quickly on the exam, which will free up valuable time and help increase your overall score.
GMAT Data Sufficiency Overview
First of all, you may be wondering, how many data sufficiency questions are on the GMAT? Out of the 31 total question in the GMAT Quantitative Reasoning section, approximately 8-11 are data sufficiency problems. In other words, somewhere around 25%-33% of your quant score (or 13%-17% of your total GMAT score) will be determined by your performance on data sufficiency questions. The balance of the remaining quant section consists of 20-23 questions of the more familiar ‘Problem Solving’ style.
You’ll have 62 minutes to complete the 31 quantitative section questions, which works out to 2 minutes per question. However, most students tend to take a little bit longer amount of time on average to complete GMAT data sufficiency questions. This is particularly true for hard, 700-800 level data sufficiency problems.
What is GMAT Data Sufficiency?
Arguably, data sufficiency questions are the GMAT’s best assessment of your business management skill set. As an investor, manager, or consultant you rarely have a complete, perfect set of information, and you especially don’t have the time and resources to acquire it.
What the data sufficiency section of the GMAT tests is whether you have enough information to make a decision (Yes/No) or answer a specific question (Value).
Every data sufficiency question will include two pieces of information (or Statements) that are clearly labeled (1) and (2).
This question type is designed to trick your process of reasoning, and there’s no shortage of options at the question writer’s disposal to accomplish their task. This leads us to our first GMAT data sufficiency tip:
Data Sufficiency Tip #1: For Yes/No questions, recognize and remember that “sometimes yes” and “sometimes no” is not good enough. “Always” is mandatory for sufficiency.
For example, consider the question: “Is Elise’s dog a puppy?” Two statements are given:
- A puppy is a dog less than or equal to 3 years of age
- Elise got her dog less than 3 years ago
Elise may have gotten her dog when it was a puppy. However, she may also have adopted her dog when it was an adult. Thus, we don’t have sufficient information to answer this yes/no question, and we can confidently say additional information is necessary to definitely answer it.
GMAT Data Sufficiency Answer Options
This brings us to our second tip, which can save test takers a lot of time and eliminate confusion.
Data Sufficiency Tip #2: Memorize the 5 Data Sufficiency Answer Choices. They are always the same, and the order never changes!
You can remember the answer choice options (and order) through this handy data sufficiency mnemonic: (1)-(2)-(T)-(E)-(N). See the full breakdown below to understand the range of answer choices from ‘A’ through ‘E’:
- Statement (1) alone is sufficient to answer the question; Statement (2) alone is not
- Statement (2) alone is sufficient to answer the question; Statement (1) alone is not
- Only when considered together (T) do you have sufficient information to answer the question
- When considered individually, either (E) statement provides sufficient information to answer the question
- When considered alone or together, neither (N) statement provides sufficient information to answer the question
Committing the 5 data sufficiency answer options to memory alone will help keep you out of the bottom 20% of test takers on the GMAT quant section. From here, the next biggest leg up on your competition can be made by always doing the following:
Data Sufficiency Tip #3: Evaluate each of the two statements individually prior to assessing them together.
This is one of the most common ways the question writers like to trip you up. It’s critical that the only time you use all the available information from statements (1) and (2) is after you’ve fully determined they were both insufficient on their own. If you avoid this common mistake, you’ll easily do better than the bottom one-third of exam takers.
For more helpful GMAT tips like these, try out the Magoosh GMAT review course free trial.
Data Sufficiency GMAT Practice Questions
To introduce our remaining two tips, let’s now take a look at a couple of real, GMAT exam-like data sufficiency practice questions.
Is z >= 1/z ?
(1) z is positive
(2) |z| >= 1
A. Statement (1) ALONE is sufficient, but Statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but Statement (1) alone is not sufficient to answer the question asked.
C. Both Statements (1) and (2) TOGETHER are sufficient to answer the question asked; but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient to answer the question.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
Number properties is one of the most frequently tested topics on the GMAT quant section. The test writers love to trick students on this topic, and it’s critical for you to recognize that a “number” can be any of the following:
- Positive
- Negative
- Zero
- Fraction
- Square Root
- Decimal, pi, etc.
Data Sufficiency Tip #4: Test by plugging in “numbers of all types.”
For the above question, you can rule out Statement (1) by plugging in a positive fraction. Note, students who only plugged in positive integers would have incorrectly assumed Statement (1) alone was sufficient. For Statement (2), plugging in both positive and negative numbers leads to opposing conclusions, so (2) is also insufficient. Only when combining together (T) the two statements do we achieve sufficiency. Hence, Answer C.
Still Feeling Stumped With Data Sufficiency?
Let’s try one more data sufficiency example question.
What is the total cost of 10 identical moka pots and 10 identical french presses?
(1) 3 moka pots and 2 french presses cost a total of $130
(2) moka pots and 3 french presses cost a total of $120
A. Statement (1) ALONE is sufficient, but Statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but Statement (1) alone is not sufficient to answer the question asked.
C. Both Statements (1) and (2) TOGETHER are sufficient to answer the question asked; but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient to answer the question.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
Data Sufficiency Tip #5: Avoid the temptation to calculate the answer. You don’t need to know the exact answer. You only need to know whether there is sufficient information to answer the question.
Many students will rush into attempting to calculate the answer to the above question. You may recognize how you could build an equation for each of the two statements. Don’t fall into the trap of solving for the system of equations. Simply recognize that by combining together (T) the two statements, you have sufficient information to answer the question. Therefore, Answer C.
5 Essential GMAT Data Sufficiency Tips
As a review, here’s the full list of our essential GMAT data sufficiency tips:
- Sometimes yes and sometimes no means “not sufficient.”
- Memorize the 5 data sufficiency answer choices. They never change.
- Evaluate each statement alone before assessing them together.
- Test by plugging in “numbers of all types.”
- Don’t waste time calculating an answer unnecessarily.
The best way to approach data sufficiency problems on the GMAT is to follow a systematic, repeatable process using the above essential tips. With deliberate practice, you’ll be able to work past the unfamiliarity and feel more at ease than most with data sufficiency questions.
How to Improve Your Data Sufficiency GMAT Skills?
Hopefully by now you have a solid grasp of this unique question style and have picked up a few data sufficiency tricks. If you’re still somewhat uneasy with these questions, check out the GMAT Club’s 100 easiest data sufficiency questions. This is a great list of practice questions to develop confidence in your skills by focusing on the question structure rather than advanced quantitative topics.
If you’d like to learn more and truly master data sufficiency on the exam, consider taking an on-demand GMAT prep course. Online review courses are more affordable than you might think and provide the best bang for your buck among GMAT prep materials. Good luck studying and don’t forget about (1)-(2)-(T)-(E)-(N)!