Data sufficiency questions are tricky, many people misinterpret the concept of these questions and suffer because of this particular type. Keep in mind these 5 points when you attempt Data sufficiency questions.
1. Do not waste valuable time solving a problem.
You only need to determine whether sufficient information is given to solve it.
2. Consider each statement separately.
First, decide whether each statement alone gives sufficient information to solve the problem. Be sure to disregard the information given in statement (1) when you evaluate the information given in statement (2). If either, or both, of the statements give(s) sufficient information to solve the problem, select the answer corresponding to the description of which statement(s) give(s) sufficient information to solve the problem.
3. Judge the statements in tandem if neither statement is sufficient by itself.
It is possible that the two statements together do not provide sufficient information. Once you decide, select the answer corresponding to the description of whether the statements together give sufficient information to solve the problem.
4. Answer the question asked.
For example, if the question asks, “What is the value of y ?” for an answer statement to be sufficient, you must be able to find one and only one value for y. Being able to determine minimum or maximum values for an answer (e.g., y = x + 2) is not sufficient, because such answers constitute a range of values rather than the specific value of y.
5. Be very careful not to make unwarranted assumptions based on the images represented.
Figures are not necessarily drawn to scale; they are generalized figures showing little more than intersecting line segments and the relationships of points, angles, and regions. So, for example, if a figure described as a rectangle looks like a square, do not conclude that it is, in fact, a square just by looking at the figure.
Lets take an example of Quant and Logic based DS.
Directions to Solve
In each of the questions below consists of a question and two statements numbered I and II given below it. You have to decide whether the data provided in the statements are sufficient to answer the question. Read both the statements and
(A) If the data in statement I alone are sufficient to answer the question, while statement II are not
(B) If the data in statement II alone are sufficient to answer the question, while statement I are not
(C) If the data either in statement I alone or in statement II alone are sufficient to answer the question
(D) If the data given in both statements I and II together are not sufficient to answer the question and
(E) If the data in both statements I and II together are necessary to answer the question.
Quant based Data Sufficiency
1. How long will Machine Y, working alone, take to produce x candles?
I. Machine X produces x candles in 5 minutes.
II. Machine X and Machine Y working at the same time produce x candles in 2 minutes.
A. I alone sufficient while II alone not sufficient to answer
B. II alone sufficient while I alone not sufficient to answer
C. Either I or II alone sufficient to answer
D. Both I and II are not sufficient to answer
E. Both I and II are necessary to answer
Answer: Option E
I. gives, Machine X produces x/5 candles in 1 min.
II. gives, Machine X and Y produce x/2 candles in 1 min.
From I and II, Y produces x/2 – x/5 = 3x/10 candles in 1 min.
3x/10 candles are produced by Y in 1 min.
x candles will be produced by Y in 10/3 min
Thus, I and II both are necessary to get the answer.
Correct answer is (E).
Logic Based Data Sufficiency
1. Question: In which year was Rahul born ?
I Rahul at present is 25 years younger to his mother.
II Rahul’s brother, who was born in 1964, is 35 years younger to his mother.
A. I alone is sufficient while II alone is not sufficient
B. I alone is sufficient while I alone is not sufficient
C. Either I or II is sufficient
D. Neither I nor II is sufficient
E. Both I and II are sufficient
Answer: Option E
From both I and II, we find that Rahul is (35 – 25) = 10 years older than his brother, who was born in 1964. So, Rahul was born in 1954.