Data Sufficiency : Concepts and Theory

About Data Sufficiency
In data sufficiency problems, a question comprises of two statements labelled I and II, which contain certain data. In these questions, the crucial point is that you need not to solve the question but to check whether the data given in the statements are sufficient to solve the question or not. The statement will be considered sufficient if the answer you obtain is unique. If a question cannot be solved with the help of the statement/statements or it has multiple answers, then the given statements would be insufficient.
Understanding Data Sufficiency Answer Options
Every Data sufficiency problem has two statements and a question, in which certain information is given. You need to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements, your knowledge of mathematics and everyday facts (such as the number of days in June or the meaning of counterclockwise), you should mark your answer as:
  1. If statement I is sufficient to answer the question, but statement II alone is insufficient.
  2. If statement II is sufficient to answer the question, but statement I alone is insufficient
  3. If both statements I and II together are sufficient to answer the question, but neither statement alone is sufficient;
  4. If each statement alone is sufficient to answer the question;
  5. If statement I and II together are not sufficient to answer the question, and additional data is required to solve the problem. 
Steps to Solve Data Sufficiency
Let us use Data sufficiency tricks to solve DS problems. The first step is to consider each statement as individual statement i.e. treat each statement as independent statements.
To solve the question, take the first statement and check whether the question can be solved using this statement alone. If you get a confirmed answer from the first statement, then we have either (a) or (d) as the answer.
Now come to the second step. Consider the second Statement. If the second statement is independently sufficient to solve the question then this statement is also valid. Mark your answer accordingly i.e. option (d) otherwise mark Option (a) as the answer.
Now if 1st Statement is not sufficient to solve the Question but 2nd Statement is alone sufficient to solve the question then (b) is your answer.
There is a possibility that neither statement alone has the required information to solve the question, but when both statements are combined then the Question can be solved. In that case (c) is the correct answer option.
Quite possibly, you may be unable to solve the problem with the help of given data individually or even by combining both statements, then the answer will be ,”data insufficient to solve the problem”.
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