Data Sufficiency

Please can someone explain the question and answer?
Thanks

The initial info that (-a, b) and (-b, a) are in the same quadrant tells us that the pairs of numbers {-a, -b} and {b, a} share the sign: if a is positive, then so is b; if a is negative, then so is b. This makes for two cases:
a. when a and b are both positive
b. when a and b are both negative.
We can't tell if it's one case or the other, but that is not relevant.

Now, let's look at the stmts:
1. tells us that x and y share the sign, which is a good start, but since we cannot establish if x and y share the sign of a and b, we can't establish if (-x, y) is in the same quadrant as the above points.

2. gives us the extra info that we need to complete 1: it's basically telling us that a and x (and by using 1) and consequently all the numbers share the same sign.
This is why [spoiler]C[/spoiler] is the answer here: only after putting both stmts together we are able to conclude that the numbers share the sign, no matter what sign it is.

I've also attached smth about quadrants, it may come in handy.

Thanks yet again DanaJ - your explanation was very helpful, clear and I was able to understand where I made the mistake!

DanaJ wrote:
I've also attached smth about quadrants, it may come in handy.

You might want to correct the 2nd quadrant details. X is negative & Y is positive in the 2nd quadrant.

Oops... yes, you are right. I missed that.

I have just thanked "DanaJ" for the following post, "Quadrant question - gmat prep" .

I have just thanked "logitech" for the following post, "Quadrant question - gmat prep"
... for being so supportive!

You get my first "thanks". Cheers.

I have just thanked both of you ... No Reason

Oh look a admin spamming