DS Format and the Five Answer Choices
Data Sufficiency questions ask: "Do you have enough information to answer the question?" You don't need to solve — just determine if a unique answer is possible.
Core DS Decision Strategy
| If Stmt (1) is... | If Stmt (2) is... | Answer |
|---|---|---|
| Sufficient | Sufficient | (D) |
| Sufficient | Not sufficient | (A) |
| Not sufficient | Sufficient | (B) |
| Not sufficient | Not sufficient, but together sufficient | (C) |
| Not sufficient | Not sufficient, together also not sufficient | (E) |
Always evaluate statements INDEPENDENTLY first. Cover one statement while checking the other. Never let one statement influence your assessment of the other.
Value Questions vs Yes/No Questions
Ask for a specific value (e.g., "What is x?"). A statement is sufficient if it gives exactly one possible value for x. If x could be 3 or 7, the statement is NOT sufficient.
Ask whether a condition holds (e.g., "Is x even?"). A statement is sufficient if the answer is always yes OR always no — a consistent answer either way. "Sometimes yes, sometimes no" = insufficient.
Advanced DS Patterns
10 Data Sufficiency Traps
1. Evaluate statements INDEPENDENTLY
Never read statement 2 and let it help you evaluate statement 1. Cover each with your hand.
2. Value: need exactly one answer; Yes/No: need always-same answer
Different tests for different question types.
3. "Sufficient" ≠ "I calculated the answer"
You only need to know you COULD calculate it — uniquely. Stop early if you see you can.
4. $x^2 = 4$ does NOT determine x
$x = 2$ or $x = -2$ — two solutions means insufficient for a value question.
5. Consistent constraints from the question stem apply to both statements
If the question says "positive integer," remember that when evaluating each statement.
6. Don't pick (C) just because statements look complementary
They might each be sufficient alone — the answer might be (D).
7. "Always" is the key word in Yes/No
A statement is sufficient for Yes/No only if you get the same answer for every valid case.
8. Combining statements: only try (C) after ruling out A, B, D
Don't jump to combining. Work through (A), (B), (D) first.
9. Sufficient can mean the answer is NO
In a Yes/No question, if the answer is ALWAYS NO, that's still sufficient.
10. Don't solve — determine sufficiency
Many test-takers waste time solving fully. Stop when you know a unique answer exists.
10 GMAT Practice Questions
What is the value of $x + y$?
(1) $x = 7$
(2) $x + y = 2y - 3$
(C) Both together sufficient. (1): $x=7$ but we don't know $y$. NOT sufficient. (2): $x+y = 2y-3$ → $x = y-3$, but doesn't give a unique value of $x+y$. NOT sufficient. Together: $x=7$ and $x=y-3$ → $y=10$ → $x+y=17$. Sufficient. (C).
Is $n$ odd?
(1) $n^2$ is odd.
(2) $2n + 1$ is even.
(A) Statement (1) alone sufficient. (1): $n^2$ odd → $n$ must be odd (even squared is even). Sufficient. (2): $2n$ is always even. $2n+1$ is always odd — NOT even. Statement (2) is a contradiction (never even) → consistent with $n$ being anything (statement is never satisfied). But actually, $2n+1$ is always odd regardless of $n$, so this gives no information. NOT sufficient. Answer: (A).
What is the value of $|x|$?
(1) $x^2 = 16$
(2) $x > 0$
(A) Statement (1) alone sufficient. (1): $x^2=16$ → $x=4$ or $x=-4$ → either way $|x|=4$. The value of $|x|$ is uniquely determined. Sufficient. (2): $x>0$ but no value given. NOT sufficient. Answer: (A).
Is $x$ divisible by 6?
(1) $x$ is divisible by 12.
(2) $x$ is divisible by 4.
(A) Statement (1) alone sufficient. (1): $x$ divisible by 12 → $12=4\times3=2^2\times3$, which includes both 2 and 3, so divisible by 6. Always YES. Sufficient. (2): div by 4 means div by 2, but might not be div by 3 (e.g., $x=4$). NOT sufficient. Answer: (A).
Is the product $ab$ negative?
(1) $a < 0$
(2) $b > 0$
(C) Both together sufficient. (1): $a<0$ but sign of $b$ unknown. NOT sufficient. (2): $b>0$ but sign of $a$ unknown. NOT sufficient. Together: $a<0$ and $b>0$ → $ab<0$. Always YES. Sufficient. (C).
What is the value of $y$?
(1) $y^2 - 9 = 0$
(2) $y > 0$
(C) Both together sufficient. (1): $y=3$ or $y=-3$. Two possible values → NOT sufficient for a value question. (2): $y>0$ — doesn't determine $y$. NOT sufficient. Together: $y=3$ or $y=-3$ AND $y>0$ → $y=3$. Unique answer. Sufficient. (C).
Is $m + n > 0$?
(1) $m > 0$
(2) $n > 0$
(D) Each alone sufficient. (1): $m>0$ but $n$ could be very negative. If $n=-100$, $m+n<0$. NOT sufficient. (2): same issue for $m$. NOT sufficient. Together: $m>0$ and $n>0$ → $m+n>0$. Always YES. (C). Wait — together is needed. Answer: (C).
If $x$ is an integer, what is the value of $x$?
(1) $-2 < x \leq 3$
(2) $1 \leq x < 2$
(B) Statement (2) alone sufficient. (1): $x$ could be $-1, 0, 1, 2, 3$. Multiple values. NOT sufficient. (2): $1 \leq x < 2$ and $x$ is integer → $x=1$. Exactly one value. Sufficient. Answer: (B).
Is quadrilateral ABCD a square?
(1) All four sides of ABCD are equal.
(2) All four angles of ABCD are 90°.
(C) Both together sufficient. (1): Equal sides = rhombus, not necessarily a square (could be a non-rectangular rhombus). NOT sufficient. (2): All angles 90° = rectangle, not necessarily square. NOT sufficient. Together: equal sides AND all right angles → square. Sufficient. (C).
For positive integers $m$ and $n$, is $\dfrac{m}{n}$ an integer?
(1) $4m = 7n$
(2) $m = 7k$ for some positive integer $k$.
(A) Statement (1) alone sufficient. (1): $4m = 7n$ → $\frac{m}{n} = \frac{7}{4}$. This is NOT an integer — definitively NO. Sufficient. (2): $m = 7k$ means $m$ is a multiple of 7, but $n$ could be any positive integer. $\frac{m}{n}$ might or might not be an integer. NOT sufficient. Answer: (A).
Lesson Summary — Key Takeaways
Evaluate independently — always
Cover each statement while testing the other. Never let one statement inform the other.
Value: exactly one possible value
Two possible values = insufficient. $x^2=4$ gives $x=±2$ = insufficient for "What is x?"
Yes/No: always same answer
Must be always YES or always NO. "Sometimes yes" = insufficient.
Sufficient NO is still sufficient
If statement proves the answer is definitively NO, choose the matching letter.