Understand and crack Data Sufficiency in CAT Examination

The problems under this domain test the ability of the student to find out whether a given set of data is sufficient to answer the question asked. There is no requirement of finding a solution to the problem. It is enough if you are able to conclude whether the question can be or cannot be answered.

Such questions, usually, fall under one of the two categories of the domain, namely — mathematical or logical/ analytical (logic as we use in day-to-day dealing).

FORMAT OF THE PROBLEM

The data sufficiency problem is distinct in its structure and format. It has a stem followed by two statements, labeled I or II. Each of the statements carries certain information related/unrelated to the problem. The candidate is to determine whether the information given in the statements can be taken — alone (i.e. I alone or II alone) or in combination (i.e. I and II together)and based on this the candidate has to conclude whether the problem can be or cannot be solved with the given information in the statements.It is extremely important to read, understand and follow the instructions given for attempting the Data Sufficiency problems.

Let us solve a problem and see for ourselves how it works!

DIRECTIONS for question 1: Each question is followed by two statements, I and II. Answer each question using the following instructions:

Choose [1]  if the question can be answered by using one of the statements alone, but cannot beanswered using the other statement alone.

Choose [2]  if the question can be answered by using either statement alone.

Choose [3]  if the question can be answered using both statements together, but cannot be answeredusing either statement alone.

Choose [4]  if the question cannot be answered even by using both the statements together.

Problem 1

What is the value of a if 10a-b = 14 ?…Note: This is the stem

I.    b = 6

              ....this is statement I

II.  a = (b-1)/5 .... this is statement II

Solution
If we take the Stem of the question and Statement I, we have —

10a - 6 = 14  (Substituting the value of b from Statement I in the expression given in the Stem), from this it is clear that we can find the value of a (which will be equal to 2).  Therefore, statement I alone is sufficient to arrive at an answer (this means our possible answers to the question can be options [1], [2] or [3]. Clearly, option [4] is eliminated.

Now, let us take the Stem and Statement II, we then have —

10a - (5a+1) = 14  (Substituting the value of b from Statement II in the expression given in the Stem), from this it is clear that we can find the value of a (which will be equal to 3). Therefore, statement II alone is also sufficient to arrive at an answer (this means our possible answer to the question can now be option [2] only. Clearly, options [1] and [3] are eliminated.

As you may have observed in the worked solution above, it is better to keep eliminating the options that do not conform to the answer…to actually arrive at the answer.