GMAT Quantitative Reasoning: Data Sufficiency
Data Sufficiency questions, which also appear in the Quantitative section, are designed to test your reasoning ability. Like the Problem-Solving questions, they require you to have a basic knowledge of the principles of arithmetic, algebra, and geometry. Each Data Sufficiency question consists of a mathematical problem and two statements containing information relating to it. You must decide whether the problem can be solved by using information from: (A) the first statement alone, but not the second statement alone; (B) the second statement alone, but not the first statement alone; (C) both statements together, but neither alone; or (D) either of the statements alone. Choose (E) if the problem cannot be solved, even by using both statements together. Usually 18 of the 37 questions on the Quantitative section of the GMAT are Data Sufficiency problems. Approaching these problems properly will help you achieve a high score. As in the Problem-Solving section, time is of the utmost importance. Approaching Data Sufficiency problems properly will help you use this time wisely.
Q. Is x greater than zero?
(1) x4 - 16 = 0
(2) x3 - 8 = 0
(A) Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
(B) Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
(C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
(D) EACH statement ALONE is sufficient.
(E) Statement (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed.
(B) STATEMENT (1) alone is not sufficient since x4 - 16 = 0 has two solutions. The first solution, x = 2, is greater than 0. The second, x = -2, is less than 0. STATEMENT (2) alone is sufficient since the only solution to the equation x3 = 8 is 2.