For those who are attempting to ace the GMAT data sufficiency section.You can read this small article on how to understand the question effectively.

Understanding GMAT data sufficiency question
Many students feel that they make more errors in DS than problem solving. Let us understand this question type in depth.

Sample question:
What is the value of a?
(1) 3a + 2b = 15
(2) b = (-3/2) (a - 5)

The Directions:
Each data sufficiency problem consists of a question and two statements, labeled (1) and (2), that give data. You have to decide whether the data given in the statements are sufficient for answering the question.

Use the data given in the questions plus your knowledge of mathematics and everyday fact, you must indicate whether the data given in the statements are sufficient for answering the questions and then indicate one of the following answer choices:
(A) Statement (i) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked;
(B) Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked;
(C) BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient;..

more here https://letsgmat.blogspot.in/2016/10/und ... iency.html

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