GMAT Sample Questions Explained - How To Approach Data-Sufficiency

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GMAT Sample Questions Explained - How To Approach Data-Sufficiency

Data-Sufficiency questions look like the evil offspring of the Problem Solving section and Critical Reasoning section: Math question stems are followed by a series of logical constructions in the answer choices.  It’s no surprise then that this strange combination worries most test takers, especially given the absence of discrete answer choices as found in typical math questions.

However, because you don’t have to solve for a specific answer, you can eschew a lot of the computational headache involved in some Problem Solving questions, and with a little know-how and practice, you can use the format of Data-Sufficiency GMAT questions to your advantage.

Since each Data-Sufficiency has the same answer choices, you can approach each methodically and quickly eliminate wrong answer choices.  A solid Data-Sufficiency strategy is to work step by step through each problem, evaluating each statement in turn and crossing off wrong answer choices as you proceed.

Practice GMAT sample questions one step at a time

As a general rule, after considered what the question stem is asking, evaluate statement 1 first.   Test whether statement 1 is sufficient by itself to solve the question stem or not, i.e. if statement 1 provides enough information to solve the problem independently of statement 2.

If statement 1 is sufficient to answer the problem, then you know that the correct answer must be either A — that only statement 1 provides enough information to solve the problem — or D — that either statement 1 or statement 2 is enough to solve the problem.  All the other answer choices can be eliminated because they state that statement 1 is insufficient, which would be false in this case.

After finding that statement 1 is sufficient, separately test statement 2.  If statement 2 is sufficient by itself, then the correct answer is D; if it’s not sufficient then answer A is correct.

Alternatively, if you test statement 1 and it turns out to insufficient, you can then eliminate answer choices A and D.  This leaves you with choices B, C and E.  If statement 2 proves to be sufficient, stop here — answer choice B is correct as statement 2 is the only information sufficient to solve the problem.

If statement 2 is not sufficient, you have a little more work to do.  Next check to see if statement 1 and 2 together provide enough info to solve the problem.  Remember, you often do not need to solve the actual problem.  Rather, you only need to determine whether it’s solvable given the information.  If the problem is solvable with both statements, answer C is correct; if not, choose answer E.

For an example of this process, check out the GMAT sample question below.  Try to solve the sample question yourself before checking the explanation.

If x and y are one digit positive integers, what is the value of x and y?

1. Sum of x and y is 8.
2. x and y are both multiples of 2.

A) Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient 

B) Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient

C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient

D) EACH statement ALONE is sufficient

E) Statements (1) and (2) TOGETHER are NOT sufficient


As discussed above, begin by evaluating statement 1:

Multiple combinations are possible for x and y: (1,7), (2, 6), (4,4) etc. Therefore, statement 1
alone is insufficient. Since statement 1 is insufficient, we can also eliminate answer choice D.  The correct answer then must be either B, C or E.

Next, evaluate statement 2:

Again, multiple values are possible for x and y: 2,4,6, and 8. Therefore, statement 2 alone is insufficient.  We now know that the correct answer is either C or E.

Now evaluate if you can solve the problem with the info contained in both statement 1 and 2.

In this case, both statements together also lead to multiple possible combinations for x and y: (2,6), (4,4), (6,2). Therefore, both statements together are also insufficient, so the correct answer can only be E, statements 1 and 2 together are not sufficient.

There you have it!  Employ this approach on all your Data-Sufficiency sample questions and this GMAT question type won’t seem as nerve-wracking.  Of course you’ll still have to know how to evaluate each statement, but by following this process, you’ll efficiently move through each question.  You can practice hundreds of Data-Sufficiency questions by downloading our free Prep4GMAT app today.

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