Data Sufficiency (DS) is unique to the GMAT. You are given a question and two statements, and you must determine whether the statements — alone or combined — provide enough information to answer the question. You do not need to solve the problem — only determine if it can be solved.

A) The Five Answer Choices (Always the Same)

• A: Statement 1 ALONE is sufficient; Statement 2 alone is not sufficient.
• B: Statement 2 ALONE is sufficient; Statement 1 alone is not sufficient.
• C: BOTH statements TOGETHER are sufficient; neither alone is sufficient.
• D: EACH statement ALONE is sufficient.
• E: The statements TOGETHER are NOT sufficient.

The AD/BCE decision tree: evaluate Statement 1 first. If sufficient → A or D. If insufficient → B, C, or E. Then evaluate Statement 2 independently.

B) What "Sufficient" Means

A statement is sufficient if it gives exactly ONE answer to the question — not two or more possible answers. Critically: if the unique answer is "no," that is still sufficient. "Sufficient" means deterministic, not "gives a useful or positive answer."

• Is x > 5? If x can only be 7 → sufficient (yes). If x can only be 3 → sufficient (no). If x could be 3 or 7 → NOT sufficient.
• What is x? If x = 4 uniquely → sufficient. If x could be 4 or −4 → NOT sufficient.

C) Evaluate Statements Independently First

A critical rule: when evaluating Statement 2, ignore Statement 1 completely. Test-takers frequently contaminate S2 evaluation with S1 information. Cover Statement 1 mentally when evaluating Statement 2.

D) Yes/No Questions

For yes/no questions, a statement is sufficient if it always gives the same answer — always yes OR always no. A statement that gives yes for some values and no for others is NOT sufficient.

E) Arithmetic and Algebraic Traps

• Integer assumption: do not assume a variable is an integer unless stated.
• Positive assumption: do not assume a variable is positive. Test negatives and zero.
• Division by variable: cannot divide both sides by a variable without knowing its sign and that it is non-zero.
• Squaring: x² = 9 → x = 3 or x = −3. Never assume positive root only.
• Dependent equations: two equations for two unknowns may look independent but be equivalent (same line). Check whether they are truly independent before concluding Answer C.

F) Number of Equations vs. Variables

For a unique solution: typically need n independent equations for n unknowns. However:

• Two equations can be identical (dependent) → not truly two equations.
• Non-linear equations can have multiple solutions even with two equations and two unknowns.
• Integer constraints (or other restrictions) can make a system uniquely solvable with fewer equations than expected.

G) Strategy Framework

1. Read the question: identify what is being asked (value, yes/no, range?) and any constraints in the question stem.
2. Evaluate Statement 1 alone. Sufficient? → A or D. Insufficient? → B, C, or E.
3. Evaluate Statement 2 alone (ignore S1). Sufficient? → D or B. Insufficient? → C or E.
4. If both alone are insufficient, try combining both statements → C or E.
5. When combining, ask: "Together, do these statements leave any ambiguity about the answer?"

H) Common DS Patterns

• Slope trap: Statement 1 gives the slope of a line and Statement 2 gives a point — together you can find the equation (C). Neither alone is sufficient.
• Remainder trap: knowing x mod 3 = 1 and x mod 4 = 2 together may uniquely determine x within a range.
• Range question: "Is 5 < x < 10?" — a statement giving x = 7 is sufficient (yes). A statement giving x > 3 is insufficient (x could be 4 or 20).

I) The C-Trap (700+ Level)

When both statements together obviously solve the problem, the instinct is to pick C. But this is a deliberate trap. When C looks obvious, test each statement alone very carefully — one of them may already be sufficient on its own, making the answer A, B, or D.

If you find yourself saying "obviously I need both," slow down. That obviousness is the trap.

J) DS Quick Triggers

Use these shortcuts to quickly assess sufficiency:

• 2 independent linear equations + 2 variables → solvable (but verify the equations are not identical)
• 1 equation + 1 variable → usually sufficient; watch for quadratics giving 2 roots (may be insufficient if both roots are valid)
• Quadratic yields 2 roots → insufficient unless context (e.g., "positive integer") rules out one root
• Ratio given without totals → insufficient for absolute values (e.g., ratio of boys to girls doesn't tell you how many there are)
• Percent without a base → insufficient for absolute values
• Even/odd constraint + linear equation → may uniquely determine a solution that algebra alone cannot

K) DS Keyword Signals (Question Stem)

• "What is the value of x?" → Value question. Need exactly ONE number. A range or inequality is NOT sufficient.
• "Is x > 5?" / "Is n prime?" → Yes/No question. Need a definite "always yes" OR "always no." Sufficient either way.
• "Is it possible that x = 3?" → Yes/No question. One case where x = 3 is possible → sufficient (yes).
• Data constraints to catch in stem: "integer," "positive," "distinct," "nonzero," "consecutive," "prime," "at least," "at most," "exactly," "no more than."

L) ZONE-F Testing (Number DS)

For number-property DS questions, systematically test these cases to find a counterexample that proves a statement insufficient:

Zero · One · Negative · Extreme (very large/small) · Fraction (between 0 and 1, also negative fractions)

If you can produce two different answers using two of these cases, the statement is insufficient.

M) Common Traps

• Apparent sufficiency from one number: a statement like "x = 5" seems sufficient, but if the question asks "what is x + y?", knowing only x is not enough unless y is also determined.
• Forgetting that sufficient means a unique answer: if a statement gives a range of possible values, it is not sufficient even if all values seem reasonable.
• Combining statements when testing individually: always re-read Statement 1 as if Statement 2 doesn't exist when evaluating Statement 1 alone.
• Confusing "not sufficient" with "the answer is No": in Yes/No DS questions, a statement that consistently gives "No" IS sufficient. Insufficient means you cannot determine whether the answer is Yes or No.
• Don't assume images are drawn to scale: geometric figures may be intentionally misleading. Work from given statements and definitions, not from visual appearance.