Bunuel wrote:
If x^3 < x^2, which of the following must be negative?
A. x
B. −x
C. x^5
D. x − 1
E. x^(−1)
Alternatively, we can TEST some values.
We're told that x^3 < x^2
So, one possible value is x =
-1Now let's test the answer choices. We get:
A.
-1, which is negative. KEEP
B. −(
-1) =1, which is positive. ELIMINATE
C. (
-1)^5 = -1, which is negative. KEEP
D. (
-1) − 1 = -2, which is negative. KEEP
E. (
-1)^(−1) = 1/(-1) = -1, which is negative. KEEP
Okay, we're still left with A, C, D and E
We need to test another value.
Another possible value is x =
1/2Test the remaining answer choices...
A.
1/2, which is positive. ELIMINATE
C. (
1/2)^5 = 1/32, which is positive. ELIMINATE
D. (
1/2) − 1 = -1/2, which is negative. KEEP
E. (
1/2)^(−1) = 2/1 = 2, which is positive. ELIMINATE
By the process of elimination, the correct answer is D
Cheers,
Brent
_________________
Brent Hanneson – Creator of gmatprepnow.com
I’ve spent the last 20 years helping students overcome their difficulties with GMAT math, and the biggest thing I’ve learned is…
Students often get questions wrong NOT because they lack the skills to solve the question, but because they don’t understand what the GMAT is testing Learn more