Great explanation, guys!
And one thing that comes up in this problem that you could use (I'm not sure how often it would come up, but here it's a nice clue) is this:
If you're saying that the answer is D, then there's really no use for the statements. You'd be able to get D even if the statements were pure gibberish. From the stimulus we know that s^4 must be positive (it's an even exponent so it can't be negative, and the whole product is less than 0, so it's not 0). Which means that one of v and x is positive and the other is negative, because we have:
+ * ? * ? = negative
They can't share the same sign.
When I first looked at this, my initial inclination was D...but that was before I even looked at the statements. And that was my clue to think "wait a second...how can I solve the problem even before I get to the statements?", reconsider the setup and realize that while s^4 must be positive, s could be either positive or negative. s is the linchpin - v * x is definitely going to be negative, so it all hinges on s. And noting that the statements didn't matter in my incorrect-assumption view of the original stimulus gave me that clue that I should read it again more closely.
Like I said, I don't know how often that will come up, but if it does it's a nice clue that you need to go back and reconsider...
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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