GMAT data sufficiency tips Save precious minutes…HOW?

Save precious minutes…HOW?

Don’t calculate exact answer.

Ask: “can I find the answer?” instead of “what is the value of the unknown variable?”

Data sufficiency is a test of mathematical reasoning.  It tests your ability to evaluate the adequacy of given data in answering a question in the mathematical setting. This involves verifying the sufficiency of data to solve a problem, distinguishing between relevant and irrelevant data, and establishing relationship between variables.

Here’s how the directions for data sufficiency problems appear in the exam

A given question is followed by two statements. You are required to determine whether the statements can be used to answer the question.

Mark (A) if statement I alone is sufficient but statement II alone is not sufficient to answer the question

Mark (B) if statement II alone is sufficient but statement I alone is not sufficient to answer the question

Mark (C) if both statements I and II together are sufficient to answer the question

Mark (D) if each statement alone is sufficient to answer the question

Mark (E) if statement I and II together are not sufficient to answer the question

Let’s take a problem

In the figure above, the points A,B,C,D  and E lie on the a line. A is on both circles, B is the centre of the smaller circle, C is the centre of          the larger circle, D is on the smaller circle and E is on the larger circle. What is the area of the region inside the larger circle and outside the smaller circle?
(I) AB=3 and BC=2
(2)CD=1 and DE=4

To find the area of a circle the radius of the circle is required. The area of the circle = (pi)*radius*radius.
AB = is the radius of the inner circle
AC = is the radius of the inner circle
The required area= (area of the outer circle)-(area of the inner circle)

Lets take statement (I)
AB= 3 and BC =2. The area of the outer circle can be computed as the radius of the outer circle is AC(AB+BC).The radius of the inner circle is AB. The difference in the two areas will give the numerical answer.
It is not necessary to calculate the exact numerical value. It is just enough to know that the answer can be determined with the data given. Time can be saved.
Statement(I) alone is sufficient.

Let’s take statement (II)
CD+DE=CE=CA which is the diameter of the bigger circle.
The diameter of the smaller circle is CA+CD. The radius of the smaller circle is half the diameter. Hence the radius and the diameter of the inner circle can be computed.  As the radii of the bigger and inner circle are computed, the required area can be determined.

Statement (II) alone is sufficient.

Hence answer is D.

Questions such as “what is the value of ...?” , “determine the value of ...?“ can be attacked in this manner.