Hey Goldfinger,
Glad you solved this one! Actually, as soon as I saw this subject line I had a pretty good idea of what the question would be trying to do, and it's right in line with that isosceles triangle problem you had the other day. There's a pattern in these questions that you're posting here, and it's this:
The GMAT is giving you questions that elicit an answer that isn't what you'd expect.
Here, you'd expect that if you could have two different operations, say + or *, they would elicit two different answers. So the
difficulty is embedded in the fact that the GMAT will probably select at least one instance in which the two operations would produce the same answer. That's where the trick is likely to be, so you want to anticipate that.
Similarly, in that 45-45-90 triangle problem, the difficulty lies in the fact that your mind wants to see sqrt2 as a suffix to the value of the hypotenuse: x, x, xsqrt2. But the GMAT, knowing that, sets x equal to a multiple of sqrt 2 so that the hypotenuse has an integer value, therefore throwing you off.
So what you can learn from this is that you want to learn to anticipate where the GMAT is going to embed difficulty. You want to train yourself to think of the ways in which a concept or question type lends itself to a tricky question:
0 doesn't have a negative sign in front of it, but it's also not positive...it's neither
Inequalities with variables are tricky because you won't know whether you're multiplying/dividing by a negative
When you memorize the triangle ratios you get used to seeing the sqrt on the same side (across from 90 in 45-45-90; across from 60 in 30-60-90)
If you start anticipating the difficulty, you'll know exactly what to double-check on a lot of these problems...you'll already be thinking like the testmaker. It's like a chess match - your opponent doesn't typically expose his bishop to your queen without trying to lure you in (where is that knight lurking?), and the GMAT doesn't choose its numbers without setting some kind of trap, either.
If you're interested, this blog post exposes that topic a little further:
https://www.veritasprep.com/blog/2011/02 ... -the-gmat/
