GMAT Data Sufficiency: a complete five-answer method
Data Sufficiency asks whether the supplied information determines an answer. You may need algebra or a counterexample to decide that. The goal is to avoid unnecessary work, not to ban calculation.
Where Data Sufficiency belongs
In the current GMAT Exam, Data Sufficiency is part of Data Insights. Quantitative Reasoning contains Problem Solving questions. GMAC’s content guide lists all five Data Insights formats: Data Sufficiency, Multi-Source Reasoning, Table Analysis, Graphics Interpretation and Two-Part Analysis.
The five outcomes
- Statement 1 alone is sufficient; statement 2 alone is not.
- Statement 2 alone is sufficient; statement 1 alone is not.
- Together they are sufficient, but neither is sufficient alone.
- Each statement alone is sufficient.
- Even together they are insufficient.
Use the answer mapping provided with the question. Do not carry information from the first statement into the second when testing each separately.
Original example: a yes/no question
Is x greater than 5?
Statement 1: x² > 25.
Statement 2: x = 7.
Statement 1 alone: x could be 6, which gives “yes”, or −6, which gives “no”. Both satisfy x² > 25. The statement is insufficient.
Statement 2 alone: x is 7, so the answer is always “yes”. The statement is sufficient.
The correct outcome is statement 2 alone is sufficient, conventionally answer B. There is no need to combine the statements once these two separate evaluations identify the outcome.
A definite “no” also counts
If a statement instead said x = 2, it would still be sufficient for “Is x greater than 5?” It gives a definite “no”. Insufficient means multiple possible answers to the question remain, not that the answer is negative.
For a value question such as “What is x?”, a unique value is required. For a yes/no question, different possible values can still be sufficient if every permitted value produces the same yes/no answer.
A practice routine that checks reasoning
After each question, write a one-sentence justification for each statement. For an insufficient statement, provide two permitted cases leading to different answers. For a sufficient statement, explain why the answer cannot change. This exposes hidden assumptions more reliably than recording only the letter selected.
Compare your method with GMAC’s Data Insights strategies and practise with the official starter kit. The free study planner can reserve short review sessions. For feedback on your reasoning, explore GMAT tutoring. A small practice set should not be converted into a predicted official score.