Introduction to Data Sufficiency

 Many students have a lot of difficulty with Data Sufficiency problems. However, the mathematical knowledge and skill required to solve Data Sufficiency problems is no greater than that required to solve standard math problems. What makes Data Sufficiency problems appear more difficult at first is the complicated directions. But once you become familiar with the directions, you'll find these problems no harder than standard math problems. In fact, students usually become proficient more quickly on Data Sufficiency problems over time. Here are some tips:UNWARRANTED ASSUMPTIONS Be extra careful not to read any more into a statement than what is given. • The main purpose of some difficult problems is to lure you into making an unwarranted assumption. If you avoid the temptation, these problems can become routineELIMINATION Data Sufficiency questions provide fertile ground for elimination. In fact, it is rare that you won't be able to eliminate some answer-choices. Remember, if you can eliminate at least one answer choice, the odds of gaining points by guessing are in your favor. Try this example for starters. Are the majority of salespeople employed by AeroFlot
commissioned? (1) The number of salespeople employed by AeroFlot
......exceeds the number of employees at Delta Airlines who
......are not salespeople. (2) The percentage of AeroFlot's salespeople who are
......commissioned exceeds the percentage of employees
......at Delta Airlines who are salespeople. A. - Statement (1) ALONE is sufficient to answer the question, 
.......but statement (2) alone is NOT sufficient. B. - Statement (2) ALONE is sufficient to answer the question, 
.......but statement (1) alone is NOT sufficient. C. - BOTH statements (1) and (2) TOGETHER are sufficient to 
.......answer the question, but NEITHER statement ALONE is 
.......sufficient. D. - Each statement ALONE is sufficient to answer the question.

E. - Statements (1) and (2) TOGETHER are NOT sufficient to 
.......answer the question. Analysis Ask yourself what specific information you need in order to answer the question posed. As you consider each of the two numbered statements independently of each other, ask yourself whether the statement provides any such information. This problem involves the concept of proportion. On the GMAT expect to encounter at least two proportion questions (either Problem Solving or Data Sufficiency) altogether. Notice that no arithmetical calculations are required here. That's because Data Sufficiency problems are designed to test you primarily on concepts, not on your ability to solve a problem by working to a quantitative solution. (That's what Problem Solving questions are for.) In order to answer the question posed here, you need information about the number of commissioned salespeople relative to the number of non-commissioned salespeople. Statement (1) alone provides no such information. [You can eliminate answer choices (A) and (D).] Statement (2) alone provides a meaningless comparison between percentages of two different "wholes"; the statement provides no information about the number of commissioned salespeople relative to the number of non-commissioned salespeople (the "whole" being the total number of salespeople). Thus, statement (2) alone is insufficient to answer the question. [You can eliminate answer choice (B).] Considered together, however, statements (1) and (2) do suffice to answer the question. The correct response is (C). Statement 1 provides that more than 50% of the employees are salespeople. Statement (2) adds that this percentage is less than the percentage of salespeople who are commissioned. Thus, the percentage of salespeople who are commissioned must exceed 50%, and the answer to the question itself must be "yes." (In other words, you can answer the question considering the two statements together.) Автор: Robert Simmons, a graduate of Zicklin School of Business, is a GMAT professor and MBA Advisor at Pericles ABLE Project.