GMAT PREP - Variables

If wx = y, what is the value of xy?

Statement 1: wx^2 = 16
Statement 2: y = 4

Statement 1:
We need to find the answer of x*y. We know that y = wx. If you multiply wx (which is also equivalent to y) by x then you have wx^2. Therefore, wx^2 is equivalent to xy. Thereofre the value of xy is 16 according to statement 1. Statement 1 is sufficient.

Statement 2: y = 4. This does not provide us with any information about the value of x. We cannot determine the value of xy from this information. Therefore, this statement is insufficient.

Answer: A

Similar approach as RipRop mutlipltying by x to stmt I gives us value of xy
which is the same as wx^2 = 16

Stmt II - No info about x INSUFF

A)

I am little confused about this. I was hesitant to multiply both sides of stmt1 by x to wx^2 = xy. My reason being that we dont know anything about x, y or w. They could be +ve, -Ve, or 0.

Can u pls clarify where I can just multiply/divide by a variable (when the value of that var is not known) and where I cannot do it.

thanks
-V

Can u pls clarify where I can just multiply/divide by a variable (when the value of that var is not known) and where I cannot do it.

I think this is not an inequality.(<,>,<=,>=) etc... If it is then u r correct.

wx=y (considering case when x is negative for eg)

w = 2 x = -4 y = -8

Multiply by x on bothe sides the equality remains the same

2 * -4 * -4 = 32

-8 * -4 = 32

Hope this helps and hope I dint miss something here!


--CR

stmt 1

wx^2 = 16

=> w = 16/x^2

substuting this in the question stem , we get 16x/x2 = y => 16/x = y => 16=xy

hence stmt 1 is suff.