Data Sufficiency

Let us understand one approach to solve DS questions with lots of variables
That is substituting numbers
Here's a DS question
Is zp negative?
(1)pz4<0
(2)p+z4=14

In sums involving inequalities, substitute numbers for variables wisely. When you see the variables (i.e. a,b,c...) you would substitute numbers. For those of you who are out of touch in math, would substitute natural numbers (1,2,3,4...).
You should realize that a number could be positive, negative, zero, a fraction, square root, pi or some other decimal. The possibilities are many.
So before arriving at a conclusion check whether the inequality satisfies all the different types of number. At times the question will introduce conditions and this will limit the types of numbers which have to be substituted.
Lets take statement 1
(1)pz4<0
z=1 hence z4=1(positive) z=-1 hence z4=1(positive)
z=0.1 hence z4=0.0001(positive) z=-0.1 hence z4=0.0001(positive)
z cannot be 0 as the product pz4 has to be less than 0
z4 is always positive, but z can be positive or negative but not 0.
As the product pz4 has to be less than 0, p has to be a negative number.

Now lets analyze the product zp
z =positive p=negative zp =negative
z =negative p=negative zp =positive

Statement (1) is insufficient to answer the question as the answer is inconsistent.

(2)p+z4=14
Statement can be analyzed by framing a table.
Choose numbers such that p+z4=14
p=13 z=1 z4=1 product of zp = positive
p=13 z=-1 z4=1 product of zp = positive
p=14 z=0 z4=0 product of zp = 0 neither positive or negative
Statement (2) is insufficient to answer the question as the answer is inconsistent.

On combining both the statements
Lets frame a table
Choose numbers which satisfy pz4<0 and p+z4=14
p=-2 z=-2 z4=16 product of zp = negative
p=-2 z=-2 z4=16 product of zp = positive
Statements (1) and (2) together are insufficient to answer the question as inconsistent values can be derived. Answer E
Questions based on number properties appear on the GMAT. If you are weak on number sense, you may hastily arrive at a conclusion without checking all possibilities. Be smart at picking numbers.

Read post at https://letsgmat.blogspot.in/2016/10/gma ... itute.html

For GMAT classes @ chennai,India email me [email protected]