Gmatprep DS

The given statement says wx=y, and we want to find xy. This can also mean:

xy = x(wx) = wx^2 : Substituting y from given info.

With that, we know,

Statement (1):
this gives the exact info we need. wx^2 = 16. Sufficient.

Statement (2):
We only know y, and have no way of finding out x. Insufficient.

Answer A.

again, I totally overlooked that first statement - wx=y. A lot of these mistakes I make are very careless, or I just don't see it when I should.

Thanks termis

Well guest the answer is not C..It is A

Wx^2=16 and (wx)^2 is different

I was making the same error as you guest, but found that it is important to understand that you are trying to find xy, not just x or y.

Assuming we all agree that w=1, you will find that x can equal 4 or -4. However, if this is the case, then y will be 4 or -4 respectively.

therefore, xy will always equal 16.

I have made it a little simpler, hope it helps

wx=y

wx^2=16
wx^2=4*2^2

w=4
x=+2 or -2

if x is +2
then y=8, and xy=16

if x is -2
then y=-8, and xy=16


Hence A.

I agree, the answer should be A.

However, I went about finding the value of XY a bit differently.

If WX^2 = 16, then W=16/X^2

Substitute for W in the equation given:

(16/X^2)(X)=Y

One of the X's cancels out, which leads to...

(16/X)=Y

16=XY

I believe this way sidesteps the ambiguity of dealing with the plus or minus that comes when even powers are involved.

Good luck with the studying!