Question 154 of DS practice section from the “Official” GMAT review book (2008 version):
Stem: Is x negative?
Data:
a) x^3(1-x^2)<0
b) x^2-1<0
Based on a) -1<x<0 U x>1
Based on b) -1<x<1
Neither option is sufficient on their own; now, if we intersect both a) and b), the answer is -1<x<0. The “official” answer to this question is that C (both options combined) are sufficient to determine whether the number x is negative, HOWEVER, it is not any negative, since, for example, x = -8 does not satisfy either a) or b), and it is still negative number; so, to me this is an option E. Of course, I got it wrong, since what the GMAT guys meant to ask seems not to be what they actually asked... Or am I a too complicated thinker? I bet that two questions like this in the same exam would have different answers depending upon whomever decided what the one they wanted was.
Any comments are appreciated.
Stem: Is x negative?
Data:
a) x^3(1-x^2)<0
b) x^2-1<0
Based on a) -1<x<0 U x>1
Based on b) -1<x<1
Neither option is sufficient on their own; now, if we intersect both a) and b), the answer is -1<x<0. The “official” answer to this question is that C (both options combined) are sufficient to determine whether the number x is negative, HOWEVER, it is not any negative, since, for example, x = -8 does not satisfy either a) or b), and it is still negative number; so, to me this is an option E. Of course, I got it wrong, since what the GMAT guys meant to ask seems not to be what they actually asked... Or am I a too complicated thinker? I bet that two questions like this in the same exam would have different answers depending upon whomever decided what the one they wanted was.
Any comments are appreciated.
