10 must NOT DOs for GMAT math
The directions to Data sufficiency qns ( some tips below may require you to revisit these directions)
This problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements plus your knowledge of mathematics and everyday facts (such as the number of days in July or the meaning of counterclockwise), you must indicate whether:
A statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked;
B statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked;
C BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient;
D EACH statement ALONE is sufficient to answer the question asked;
E statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.


Now here are some simple not dos
1.
Assume that a given number is positive only. The numbers given can be zero, negative fractions or decimals.

i.e. sample
Main statement- is the modulus of X less than 3?
Sub statement 1- X(X+3) <0 Sub statement 2- X(X-3)>0
X can be zero, negative, fraction or decimal.

2.Assume that in a 'Is...( refer main st in point 1 above ) question type, no is an invalid answer. 'yes,' can be a valid answer; no can be a valid answer. 'sometimes yes and sometimes no' are invalid.


3.Ignore minimum factors required( that can be gauged from the main st) to answer the qn, if either of the sub statements do not have the min factors, automatically the ans cannot be A or B.
Main st: Is X grater than Y?
Sub st 1. X is greater than Z
Sub st 2. Y is lower than Z
Here as per directions, the ans cannot be A or B.

4.Conclude based on the outcome, while substituting a number to arrive at the answer. Check the outcome while substituting varied numbers i.e. zero,+ve integer,-ve integer,+ve fraction and -ve fraction

5.Hurriedly Mark either A (or B) as the answer option when statement 1(or 2) yields an answer. Study statement 2(or 1)also . If this also leads to answer mark D, else mark A(or B)

6.Spent time deriving absolute values when approximation is sufficient in arriving at a decision.

7.Arriving at numerical values when the question requires only counting the occurrences.

8.Attempt a complex combinatronics problem by attempting to pick/select many objects at a time. pick/select one object at a time. This doesn't change the final outcome.

9.Follow faulty logic.
i.e. A sample sum
Main statement- is the modulus of X less than 3?
Sub statement 1- X(X+3) <0 Sub statement 2- X(X-3)>0

Correct logic
Determine the range of numbers which satisfy the sub statements
Check whether these numbers satisfy the main statement.

Wrong logic
Determine the range of numbers which satisfy the main statement
Check whether these numbers satisfy the sub statements.

10.Ignoring additional information required to solve the problem
Sample problem
Main statement- A and B takes x and y days respectively to complete a work. How many days will A and B together take to complete it?
Sub statement 1 x=5
Sub statement 2 B alone takes twice as many days as A alone to complete the work

additional information on the efficiency of each person's work per day is a factor needed. If A works at 50% efficiency, A will take 10 days to complete the work.

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