Data Sufficiency

GMAT Quant

Value Questions

• VALUE: these questions require solving for one numerical value.

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• Examples:
• What is the value of x?
• How old is Megan?

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• The information in the statement is considered sufficient if a single number can be calculated. If multiple values are possible, the information is insufficient.

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Yes/No Questions

• YES/NO: these require either a yes or a no answer.

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• Examples:
• Is n divisible by 16?
• Is y<0?

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• The information in the statements is considered sufficient if a conclusive answer (either yes or no) can be reached. If the answer is maybe, the information is insufficient.

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• BEWARE OF DECIMALS/FRACTIONS/NEGATIVES/0 for such questions.

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Strategies

• Strategy #1: Rephrase
• Rephrase the question to find what really is being asked.

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• Strategy #2: Testing numbers
• Test random numbers, especially negatives, zero, and fractions to try and find conflicting answers. Some examples of test numbers: -10, -1, -½, 0, ½, 1, 10.

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• Strategy #3: Contradiction
• Remember that the two statements never contradict each other. If one statement proves the value of n to be 6, the other statement must also show n = 6.

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Common Mistakes

• Examine each statement independently. Do not carry information from one statement to another.
• Cover statement 2 with your finger while reading statement 1 and vice versa.

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• Don’t over calculate. Calculations are rarely required.
• Is x = 6? We don’t need to solve an equation to find out; we just need to check whether the equation can give a yes/no answer.

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• The 2 statements never contradict each other.
• Contradicting statements indicate a mistake in calculations/assumptions.

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• Do not assume numbers are integers unless explicitly stated.

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• Do not assume a number is not an integer or that a number can be negative, especially in a real world situation.
• Number of people has to be an integer.
• Quantities are all positive and can never be negative.

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Ask yourself the following

• What are the possible answers to the target question? Determine the type of question.
• Yes/No
• Value (a number/set of numbers)

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• Does this statement provide sufficient information to answer the target question?
• Helps to avoid common mistakes

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• What information would help to answer the target question?
• Sum/average/lengths etc.

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Summarizing Information

• Use information given in the target question to write equations.

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• Assign variables if required.

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• Only then move on to the statements.

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Rephrasing

• A different way to phrase the question to find whether the data is sufficient.

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• Target questions are ‘hidden’; rephrasing helps to simplify it.

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• Only then move on to the statements.

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• Example: Is 4x < 3x?
• Can be written as “is x < 0?”
• Can be further reduced to “is x negative?”

Geometry

• Do not estimate lengths/angles. Use only information that is explicitly stated.

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• To find one length, you must be given at least another length.

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• Sketch figure on scrap paper and add information to it.

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• Mentally grab and move points and lines without breaking any restrictions given.

Common Myths

• “Simple” equations with one variable can be solved.
• X can cancel, leading to an answer like 0 = 0.

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• Quadratic equations have two solutions.
• Repeated roots make a statement sufficient as there’s one definitive answer.

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• One equation with two variables can never be sufficient.
• one variable can cancel during algebraic simplification, or restrictions in values (must be positive etc) give one definitive answer.

• Two equations with two variables are always sufficient.
• One equation might just be the multiple of another, making them essential identical.
• Equation might end up being a quadratic, hence giving two answers instead of one definitive answer.

Choosing a statement

• Not required to examine them in any order.

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• Level of difficulty increased by:
• Making statement 1 more difficult than statement 2.
• Causing students to unintentionally carry information from statement 1 to statement 2.

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• Read both statements and consider the easier statement first.

Guessing Strategically

• Consider the easier statement.
• Decide whether it is sufficient or insufficient.
• Eliminate the wrong answer choices
• If a statement is sufficient, 3 answer choices can be eliminated, leaving you with a 50% chance of guessing correctly.

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• If the two statements provide identical information, the correct answer will be D or E.