GMAT Data Sufficiency
GMAT Data Sufficiency—Find the Reward in Your Answer!
Many test-takers find Data Sufficiency questions challenging. However, knowing certain strategies and key signals improves your chances of answering correctly.
The official example below, along with the detailed explanation, aims to guide you through the specific approach required to address Data Sufficiency questions effectively. We'll begin with an introduction to essential strategies unique to the Data Sufficiency question type, followed by a closer look at a sample problem.
Best Practices for Data Sufficiency Questions
Data Sufficiency is the most important question type in the Data Insights section. Of the 20 questions you encounter in Data Insights, 8 are usually Data Sufficiency. Additionally, it is probably easiest to gain a competitive advantage on Data Sufficiency compared to the other 4 question types (Multi-Source Reasoning, Table Analysis, Graphics Interpretation, and Two-Part Analysis). All of this means one thing: spend time learning the right approaches and strategies for GMAT Data Sufficiency!
In our curriculum we start by making sure that everyone has learned exactly what constitutes sufficiency in a given statement, and we make sure people avoid the following common rookie mistakes:
- In a "yes or no" question, a "no" is just as good as a "yes." Don't overlook the cleverly created "no" answer.
- Don't treat a "yes or no" question as if it is a "what is the value?" question. A statement can allow for many values but still be sufficient in a "yes or no" question.
- Don't accidentally carry information between statements. On data sufficiency questions, always ask yourself consciously: have I carried a tiny bit of information between the two statements?
- Don't accidentally treat the question as a statement or vice versa.
- Don't be lazy and don't make assumptions. If a statement seems insufficient, do everything you can to prove it is sufficient or vice versa. If the answer you are about to pick does not differentiate yourself from smart people, leverage harder or be more critical. Find the dopamine response!
- Recognize the common math set-ups used in Data Sufficiency. If you fall for a trap once, never fall for it again.
- Don't do unnecessary work but make sure you do enough to prove sufficiency or insufficiency.
After ironing out those common mistakes, we focus on the "4-level strategy" for avoiding cons and finding the reward in your answer. In Data Sufficiency there are two basic mistakes you can make:
- You can undervalue the information given. In this scenario, you think a statement is not sufficient, when it really is.
- You can overvalue the information given. In this scenario, you think something is sufficient when it really isn't.
To prevent these two mistakes in GMAT Data Sufficiency—the undervaluing or overvaluing of information—always consciously consider the level(s) beside the one you are going to pick. This may sound like a simple strategy, but people don't consciously do it on every question, and you will be amazed how often it will keep you from picking the "sucker" answer.
The Four Levels of Sufficiency are outlined below:
Level 1: (D) Each Statement Alone is Sufficient
Level 2: (A) or (B) One Statement Alone is Sufficient
Level 3: (C) Both Statements Together Are Sufficient, But Neither Alone Is
Level 4: (E) Both Statements Together Are Not Sufficient
As an example: at level 1, you are picking (D), which means you believe that each statement alone provides enough information to answer the question. If you are incorrect at level 1, there is only one mistake you could have made: you overvalued the information in one of the statements and the correct answer is really at level 2 (or lower).
When you miss a Data Sufficiency question, it is almost always by picking an answer that is one level away from the correct one: you have just slightly overvalued or undervalued information in one or both of the statements. Remember—data sufficiency questions are cleverly designed to make you do just that!
NOTE: if you are more than one level away from the correct answer in a GMAT Data Sufficiency question, it means you either don't understand the underlying math concept or you are misreading the question or statements (and thus it is not a "Data Sufficiency" mistake).
If you learn how to avoid common rookie mistakes and actively leverage the "4-level Strategy" to find the reward in your answer, your accuracy and efficiency will go up dramatically in Data Sufficiency.
GMAT Data Sufficiency, Sample Question #1
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Explanation
Detailed Solution
As you just learned in the Best Practices section, Data Sufficiency questions involve an interesting mix of math skills, critical reasoning, reading carefully, and spotting the con. This official example question perfectly captures all of these elements. As a first step, you should carefully organize all the given information provided in the question stem and isolate clearly what is being asked. In the question stem, you are given a revenue equation for customer A as follows, using E as the price per pound for English Stilton cheese and S for Spanish Manchego cheese:
15E + S = $438
Additionally, you are told that the price for each of these cheeses is proportional to its weight, which simply means that there is a constant and unchanging price per pound. The question is asking for the value of S and you can now evaluate each statement and apply the given equation to both:
- This statement gives you a second revenue equation for the purchase of Customer B as follows: 5E + 4S = $214.75 Since this gives you a second, unique equation using the two variables provided in the question stem, you know you can solve for each variable and find the value for S. NOTE: you should not actually figure out what the value is (would be a lot of wasted time), but you do need to make absolutely sure you can find it. This statement is indeed sufficient, so you know the answer must be (A) or (D) and there are thus only two levels to consider from the 4-level strategy discussed in the Best Practices section.
- This statement appears to also give you another unique equation for customer C that will allow you to solve for both unknowns. The question is designed for you to pick (D) and many people do just that!! Before you pick (D), you are supposed to consider any possible answer one level away, in this case (A). Also, your "bull&^% detector" should also be going off as you go to select (D): why would they make this question if (D) is the answer and how am I differentiating myself from smart people by picking it? The answer: they would not make this question as (D) is too simple of an answer. Since you are sure the first statement is sufficient, you need to figure out what kind of trick might exist in the 2nd. This point is important: you need to know mathematically when a 2nd equation with two unknowns might NOT allow you to solve for the two unknowns. When might that happen? When the 2nd equation is actually the same, often cleverly, as the first one. If you are looking for this con (and it has been used dozens and dozens of times on previous official Data Sufficiency questions) then you will notice that the equation given in statement (2) is actually the same as the equation given in the question stem. Let's compare them: 15E + S = $438 6E + S = $175.20 If you take the 2nd equation and multiply each term by 2.5 or 5/2, then you see it is identical to the given equation. By using complex numbers, the test makers make it much harder to see that the two equations are the same, but you will see it if you are aware of this common con.
Correct Answer
Since statement (2) is not giving you new information then it cannot be sufficient and the correct answer is (A).
The Importance of Official Questions for GMAT Data Sufficiency
In conclusion, mastering GMAT data sufficiency questions is key to excelling on the exam, especially given their critical role in the Data Insights section. As we've explored, understanding the nuances of data sufficiency problems and applying the right strategies can significantly impact your performance.
But a word of caution: the importance of using official GMAT questions in your preparation cannot be overstated. Unofficial questions, while widely available through textbooks and study apps, frequently fail to capture the essence and difficulty of official material, leading to missteps in preparation.
In contrast, official problems allow you to develop the specific analytical and reasoning skills required to excel on the GMAT.
Focusing on official GMAT data sufficiency questions, therefore, is not just about practice; it's about preparing in the smartest way possible. By avoiding the pitfalls of unofficial questions and embracing the complexity of official ones, you equip yourself with the knowledge and skills to tackle data sufficiency problems head-on.
If you're ready to commit to this approach, consider enrolling in the Menlo Coaching GMAT Prep Course. Our curriculum uses only official material, and our 5-week timeline for study is the most efficient on the market.
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