The AD/BCE Framework: Systematic Evaluation
Data Sufficiency (DS) is unique among standardized test question types: it does not ask for the answer to the mathematical question but asks whether the given statements provide enough information to determine the answer. This distinction is fundamental and the source of most DS errors — students evaluate whether a statement is true or whether they can compute something, rather than whether the statement uniquely determines the answer.
The correct DS evaluation framework is the AD/BCE decision tree. Step 1: evaluate Statement (1) alone, completely ignoring Statement (2). Ask: does Statement (1) provide sufficient information to answer the question definitively? If yes, the answer is A or D. If no, the answer is B, C, or E. Step 2a (if Statement 1 was sufficient): evaluate Statement (2) alone. If also sufficient, answer is D. If not sufficient, answer is A. Step 2b (if Statement 1 was insufficient): evaluate Statement (2) alone. If sufficient, answer is B. If also insufficient, evaluate both statements together. If together sufficient, answer is C. If together still insufficient, answer is E.
The single most common DS error is evaluating both statements simultaneously when Statement (1) alone is being considered. Students subconsciously use information from Statement (2) when assessing Statement (1), leading to incorrectly concluding Statement (1) is sufficient. The correction: physically cover Statement (2) when evaluating Statement (1), and vice versa. This simple discipline eliminates one of the most frequent DS error categories.
A critical conceptual distinction: for 'What is x?' questions, a statement is sufficient if and only if it yields exactly one value of x. For 'Is x positive?' questions (yes/no type), a statement is sufficient if it always yields the same answer — always yes, or always no. It is insufficient if there exist scenarios where the answer is yes and other scenarios where the answer is no. Many students mistakenly evaluate yes/no DS questions as if they were value questions, applying the wrong sufficiency criterion and making systematic errors as a result.