debmalya_dutta wrote:Firstly dont think A is the answer ..let's look at it
statement 1 :
y & z are either both negative or both positive
don't know anything about x . hence statement 1 insufficient
statement 2 :
x & y are either both negative or both positive
don't know anything about z . hence statement 2 insufficient
taking both the statement together
if from statement 1 , we say y,z are negative , then x is also negative which we can derive from statement 2 because x,y are of the same sign
in this case x(y+z) > 0
if from statement 1 , we say y,z are positive , then x is also positive which we can derive from statement 2 because x,y are of the same sign
in this case x(y+z) > 0
So , I will go with option C
Perfect solution!
From (1), we know that y and z are the same sign, but know nothing about x.
From (2), we know that x and z are the same sign, but know nothing about y.
Together, we know that all 3 are the same sign.
So, when we multiply out the expression in the question, we're always going to get a non-negative answer: sufficient.
(I say non-negative because we could have x=y=z=0 and a final answer of 0.)
