How to conquer Data Sufficiency (DS) on GMAT

DATA SUFFICIENCY (DS)

Data Sufficiency (DS) is a part of the quantitative section on the GMAT exam. As the name suggests you have to find out whether the given data is sufficient to answer the question or no. The data sufficiency question in GMAT exam is slightly different from the regular CAT data sufficiency question. It is comparatively more tricky and forms a major part of the quantitative section on GMAT.

The data sufficiency (DS) problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements plus your
knowledge of mathematics and everyday facts, you must indicate whether
A. statement (1) 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;
D. EACH statement ALONE is sufficient to answer the question asked;
E. BOTH statements (1) and (2) TOGETHER are not sufficient to answer the question asked;

The easiest way to solve this question and to avoid any confusion is to take one statement at a time. There are two parts to this questions. One is the data that is already given and the other partial data given in statements (1) and (2).

Now you have to imagine that say statement (2) does not exist and only statement (1) does. Will you able to solve the given problem now? Let me give you an example here :

1. At a certain picnic, each of the guests was served either a single scoop or a double scoop of ice cream. How many of the guests were served a double scoop of ice cream?

(1) At the picnic, 60 percent of the guests were served a double scoop of ice scream.

(2) A total of 120 scoops of ice cream were served to all the guests at the picnic.

The question asks you how many guests got a double scoop. The information you already have is that there were only two type of scoops : double and single.
Now just cover up statement (2) and see if the information in (1) is enough to answer this question. You can see that it gives only a percentage and total number of people is unknown. Hence (1) is not sufficient to answer this question.

For the same example now cover up statement (1) and see if you can answer the question. Again you can easily see that (2) gives only the total number of ice creams served. Therefore (2) also is not sufficient to answer this question.

Now see if you can answer the question using both (1) and (2). Viola!!! you can.
(1) gives you the percentage being served one kind of ice cream and (2) gives you the total number of ice creams. Using these two you can find the number of ice creams of both kinds and answer the question.

Therefore, your answer would be C.

Remember you are not supposed to find the answer in DS questions. Hence don't go about solving the whole problem and waste your time. The key is to just plug in the data given and see if you can solve for a single variable. To achieve sufficiency, there must be as many equations as there are variables.

TIPS and TRICKS for DS :

• In Data Sufficiency questions, you are usually being asked 1 of 3 things:

1. A specific value - like in the example above
2. A range of numbers
3. Yes/No or True/False whatever you may like to call it

• Start with each statement separately to see the sufficiency and if they do not satisfy the question then look at both the statements together.

• Eliminate wherever possible. For Instance if (1) is not sufficient A and D cannot be the answers so you can do better guesswork out of BCE.

• On harder DS questions, answer choices tend to be more sufficient than they might appear.
• DON’T CHOOSE (E) if you have to guess.
• Pick between (A) or (C), if you can eliminate (B).
• Historically, (A) is slightly more common as the right answer.

• About 1/3 of DS questions are YES/NO questions.

• Only about half the time do you have to look at both statements in combination.

• Do not make unwarranted assumptions. For instance for the following question :

Did Person A get over 50% of the vote?

(1) Person C got 49% of the vote.
(2) Person A got 25,000 of the 100,000 votes cast.

Most people would assume here that there are only 2 persons A and C and take (1) as sufficient. Be very careful with such type of questions and do not make this mistake of assuming the data not given.

Another common mistake people make is assuming the information given in statement (1) in solving the problem with statement (2). This is a very common exam trick and most people fall for it atleast in their initial study period. Hence view statements separately first and only when you are unable to answer the question this way take both the statements together.

On YES/NO DS questions, if a statement answers the
question conclusively in the affirmative or in the
negative, then IT IS SUFFICIENT.

Example :
Is it true that a>b?
(1) 2a > 2b
(2) a + c > b + c

You can see that both (1) and (2) can answer this question independently. Hence you should not care about any real values here. I am assuming you would be able to solve this on your own and hence not putting the explanation here.

These tricks really helped me in scoring well on DS and I hope they would be useful for you too.

To download problems for DS you can go to the download section of the blog. It contains more than enough for you to get good practice on this section! All problems come with detailed solutions and in case you find any difficulty understanding any problem you can always ping me!

Currently the download section is not ready but if you need the material immediately you can ping me again!

GMAT - Format and sections

GMAT is an aptitude test conducted worldwide as a selection criteria for entrance into many B schools. It is a computer adaptive multiple choice test. By adaptive i mean that based on your answer to a previous question, right or wrong, your next question will be tougher or easier. The GMAT consists of 3 sections :
1. Verbal
2. Quantitative
3. Analytical Writing

The GMAT is a three-and-one-half hour computer adaptive test (CAT). The exam time is divided as follows:

Section		Time
Writing	Analysis of Issue Essay	30 minutes
Writing	Analysis of Argument Essay	30 minutes
Math	37 Questions	75 minutes
Verbal	41 Questions	75 minutes

Verbal Section

The verbal section is again divided into three parts :
(i) Reading Comprehension (RC)
(ii) Sentence Correction (SC)
(iii) Critical Reasoning (CR)

Reading Comprehension

The RC section will consist of a write up of about 4-5 paragraphs (350-400 words) and you will be asked to answer questions based on the RC. The RC can be related to any topic and you need not have prior knowledge of the same. The questions will test your understanding of English words and your power to comprehend data in a given span of time. Some questions will be directly based on the passage and you just have to pick up the data from the right places in the passage. Others will be inference based and you would have to draw certain conclusions based on the data in the passage. Here is a list of sample questions to get you a feel of the way such questions would be asked : -Which of the following would most logically be the topic of the paragraph immediately following the passage?

-The primary purpose of the passage is to....?

-The passage supplies information that would answer which of the following questions?

-Which of the following, if true, would most weaken the author’s assertion?

Sentence Correction

This question of the verbal section of GMAT is to test your English Grammar basically. And believe me you would really want to go back to third standard and study Wren and Martin again!!!
You would mainly be asked to correct a sentence, that is see if it is grammatically correct in standard written English language.
The other question type will be making a sentence as compact as possible (does not mean the shortest) by removing any unnecessary words or expressions.

Some examples for the two type of questions :

Despite pleas from consumer advocate groups, the high gasoline prices of late seem like it is indicative that gasoline prices, although they have almost doubled in the past year, have not yet reached their peak.

A. like it is indicative that

B. as if to indicate

C. indicative of

D. to indicate that

E. like an indication of

The correct answer here is D according to standard English rules that I will talk about in my later posts. Remember that in SC questions the first option will always be the repetition of the exact phrase in the given sentence. It may or may not be correct. There would be questions where the given phrase is the correct phrase.

Critical Reasoning

This question on the verbal section of the GMAT tests your logic and reasoning skills. It tests whether you can understand a given set of logically connected sentences and can draw inferences based on them.

You could be asked to draw conclusions, evaluate underlying assumptions, point out any erroneous argument, correct an argument, analyze the given options and see if any of them strengthen/weaken the argument.

Let me give you a simple example here to help you understand this section better.

Monthly employee evaluations are an excellent tool for managers. With them, employees that are not productive can be removed from the company, and efficient workers rewarded, and all within the space of a month.

The argument above logically depends on which of the following assumptions?

A Workers do not in turn complete evaluations of the management of the company.

B Unproductive employees often refuse to co-operate with the managers doing the evaluations, because they see these evaluations as a violation of their privacy.

C Most studies indicate that employee evaluations have no bearing whatsoever on worker satisfaction.

D Evaluations can identify with some accuracy whether an employee is productive or not.

E Employee evaluations are a better source of information about employee grievances than are monthly staff meetings.

The correct answer for the above question is D. Now lets understand how.

Monthly employee evaluations are an excellent tool for managers - This statement is actually the conclusion of the argument(It need not be the last statement)
With them, employees that are not productive can be removed from the company, and efficient workers rewarded, and all within the space of a month. - This statement is the premise which is nothing but a statement which when combined with a logical assumption leads to the conclusion. The question asks us to find the underlying assumption on which this argument is based. On scanning through the choices you will find that only D - The most logical assumption is that this tool is infact capable of finding non productive employees. More details on the verbal section in my next post. I hope this is enough to get you started!!! Quantitative Section The GMAT quantitative section consists of two type of questions - Problem Solving(PS) and Data Sufficiency(DS) Both type of questions require basic knowledge of arithmetic, algebra and geometry.
Below is an example of a PS type question.

6. If ∠XYZ in the figure above is a right angle, what is the value of x?

(A) 155

(B) 145

(C) 135

(D) 125

(E) 110

The answer is B - 145. This was a very basic question but you might get some tricky questions on your actual GMAT paper. More on that in the detailed section later.

Let me now give you an example of a DS type of question. You will be provided with some data in the main question and some partial data in two separate options. Now you have to check whether you can answer the main question with the help of these two sub options. The question can be answered with both options exclusively, with any one of them, both of them put together or by none of them. Thats exactly what you need to find out in this question.

Here is the example :

A. statement (1) 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;
D. EACH statement ALONE is sufficient to answer the
question asked;
E. statements (1) and (2) TOGETHER are NOT sufficient
to answer the question asked, and additional data specific to
the problem are needed.

1. If today the price of an item is $3,600, what was the price of the item exactly 2 years ago?

(1) The price of the item increased by 10 per-cent per year during this 2-year period.

(2) Today the price of the item is 1.21 times its price exactly 2 years ago.

Here you can see that both options 1 and 2 can be used to answer this question exclusively. Hence you choose answer option which says that both statements can answer the question exclusively that is D.

Thats all on the format and the type of questions on all sections in GMAT. I would get back with more details and question banks on each section in my later posts.

I guess this is enough to get you accustomed to the format and sections of GMAT as of now!!