Data Sufficiency
WHAT IS DATA SUFFICIENCY?
Every Data Sufficiency problem consists of a question
followed by two statements. You have to decide NOT WHAT
THE ANSWER IS, BUT WHETHER THE QUESTION CAN BE ANSWERED
based on the information given in the two statements.
Let us take a very simple example;
What is x?
A. x + y = 17
B. 4x + 4 = 18
As in any other question in CAT, there are four alternative answer choices.
- if the question can be answered by one of the statements alone, but cannot
be answered by using the other statement alone.
- if the question can be answered by using either
statement alone.
- if the question can be answered by using both the
statements together, but cannot be answered by using
either statement alone.
- if the question cannot be answered even by using
both statements together.
Here’s how to crack it
The best way to answer Data Sufficiency problems is to
look at one statement at a time. So cover statement (B)
with your hand.
Based on statement A, x + y = 17 can we answer the question
“What is x?”
No way. If x + y = 17, there are many possible values
of x: If y equals 2, then x could equal 15. On the other
hand, if y equals 13, then x could equal 4. Statement
A is not sufficient to give us a single value for x.
Now forget you ever saw statement A. Cover it up with
your finger and look only at statement B — 4x + 4 = 18.
Based on statement B alone, can we find a single value
for x?
Yes. Using algebraic manipulation, we can do the following:
4x + 4 = 18
4x = 14
So, x = 3.5
Note that the question isn’t asking us what x equals.
The question asks only whether the information provided
is sufficient to find out what x equals. In this case
it is; statement B gives us enough information to answer
the question “What is x?” Since B is sufficient and A
is not, the answer to this question is:
- if the question can be answered by one of the statements alone, but cannot
be answered by using the other statement alone.
Note
CAT has been using different versions of what the four answer choices stand for. Therefore, it is imperative that you read the instructions given before the Data Sufficiency question in every paper and then answer them. For intance, in CAT 2003 re-test, the choices were different from what are given in the above sample. Many students who did not read the instructions carefully answered these questions wrong despite knowing how to solve them.
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