Quantitative — Data Sufficiency for the GMAT Exam

Common failure modes

These are the patterns that cause most candidates to lose marks on this topic. Recognising them in advance is half the work.

• !Solving for a specific numerical value instead of testing whether a unique answer is possible
• !Forgetting that Statement 2 must be evaluated independently before testing both together
• !Assuming constraints from Statement 1 when evaluating Statement 2 in isolation

Study tips

• 1Memorize the five DS answer choices and their logic (A, B, C, D, E) before test day — eliminate systematically.
• 2For "is X > 5" type questions, find cases where X > 5 AND cases where X ≤ 5 to prove insufficiency.
• 3Never re-use Statement 1 when evaluating Statement 2 — treat them as completely separate universes.

Sample GMAT Quantitative — Data Sufficiency questions

These sample items mirror the format and difficulty of real GMAT questions. Practice with thousands more on the free Koydo question bank.

1. 1

   Is integer n divisible by 6? (1) n is divisible by 12. (2) n is divisible by 9.

   • AStatement (1) alone is sufficient, but statement (2) alone is not sufficientCorrect
   • BStatement (2) alone is sufficient, but statement (1) alone is not sufficient
   • CBoth statements together are sufficient, but neither alone is sufficient
   • DEach statement alone is sufficient
   Why this answer?

   If n is divisible by 12, it is divisible by all factors of 12, including 6. So Statement 1 is sufficient. Statement 2 alone: n could be 9 (not divisible by 6) or 18 (divisible by 6) — insufficient. Answer: A.