### Data-Sufficiency

Example-1

Question

1. What percent of students in the class are girls?

(1) The number of boys in the class is 30.

(2) There are totally 40 students in the class.

Analysis

Let us call the main question “What percent of the students in the class are girls?” as the main question stem.

For answering this question stem, we must know,

(i) How many students in the class are girls? and

(ii) What is the total number of students in the class?

If Statement (1) is given, we only come to know the number of boys in the class as 30.

Neither of the two required data, mentioned above, can be derived from the Statement (1).

So, if Statement (1) alone is given to us,, we do not get sufficient information for us to answer the question, “What percent of students in a class are girls?”

So, (A) is not the answer.

Now, let us take Statement (2). It says that the total number of students in the class is 40. This is one of the essentially required data to answer the given question.

But, even (2) alone does not give the other required data (how many of these 40 students 40 are girls) to answer the given question.

So, Statement (2) alone is not sufficient information for us to answer the question.

So, (B) is not the answer.

Now, let us take both the Statements (1) and (2) together.

Then, we can conclude that the number of girls in the girls is 10. And they form 25% of the total number of students of the class.

Thus, we find that both statements together are sufficient to answer the question.

But neither of them alone is sufficient to answer the given question.

Therefore as per the given instructions, (C) is the answer.

Note

In this question, the percent of girls in the class is 25%. This is obvious. But we are not asked to calculate answer. We are asked only to find out whether the given data are sufficient are enough to answer the question, as per the instructions.