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GMAT Data Insights

Data Sufficiency

Decide whether the statements force one unique answer without doing unnecessary solving.

4 min

Core idea

Data Sufficiency asks one question: is the information enough?

For a value question, sufficient means exactly one value. For a yes/no question, sufficient means the information forces one definite yes or one definite no.

Solving and proving sufficiency are different tasks.

Problem Solving

Find the requested value or choice.

Data Sufficiency

Prove whether the available information determines a unique outcome.

Decision tree

Test the statements in the same order every time.

  • Test Statement (1) alone.
  • Test Statement (2) alone.
  • If both fail alone, combine them.
  • Never let information from one statement leak into the other.

Memorize the five result patterns.

A
(1) yes, (2) no
B
(1) no, (2) yes
C
Neither alone; together yes
D
Each alone yes
E
Together still no

Trap

One possible value is not enough.

If a statement allows x = 4 and x = -4, it is not sufficient for the question "What is x?" even though you found valid values.

Counterexample habit

Before calling a statement sufficient, look for a second outcome.

  • Squares can hide positive and negative roots.
  • Absolute value often creates two cases.
  • Do not assume an integer unless stated.
  • Test positive, negative, zero, and fractions when allowed.

Mini application

Try this: Is x uniquely determined? (1) x^2 = 16 (2) x > 0

Decide the sufficiency pattern before scrolling.

Solution

The answer pattern is C.

Statement (1) gives x = 4 or -4. Statement (2) allows many positive values. Together they force x = 4.

Remember this

Prove uniqueness, not just solvability.

Your last check should be: "Could another value or outcome still satisfy everything?"

Lesson 1 of 32

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