If xy ≠0, what is the value of 1/x + 1/y?
(1) 1 / (x+y) = -1
(2) xy = 6(x+y)
[spoiler]B
Why why why?? I dont get it~!
(1) 1 / (x+y) = -1
(2) xy = 6(x+y)
[spoiler]B
Why why why?? I dont get it~!
This is a great example of the utility of rewording the target question before examining the statements.gmatisgay wrote:If xy ≠0, what is the value of 1/x + 1/y?
(1) 1 / (x+y) = -1
(2) xy = 6(x+y)
If we add 1/x + 1/y, we get y/xy + x/xy which equals (x+y)/xy
So, we can reword the target question as "What is the value of (x+y)/xy?"
Statement 1:
If 1/(x+y) = -1, we know that (x+y)=-1
Is this enough information to find the value of (x+y)/xy?
No. If we replace (x+y) with -1, we get -1/xy
Since we still don't know the value of xy, we cannot answer the target question with certainty, so statement 1 is NOT SUFFICIENT
Statement 2:
If xy = 6(x+y), we can take the new target question and replace xy with 6(x+y) to get (x+y)/6(x+y), which simplifies to be 1/6
Since we are able to answer the target question with certainty, statement 2 IS SUFFICIENT and the answer is B
Cheers,
Brent
