Math questions from any Manhattan Prep GMAT Computer Adaptive Test.
praks.g
Forum Guests
 
Posts: 2
Joined: Sat Aug 25, 2012 6:44 am
 

Absolute Greater than Square

by praks.g Sun Oct 07, 2012 5:19 pm

Is x*|y| > y^2?

(1) x > y

(2) y > 0

a) Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
b) Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
c) Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
d) EACH statement ALONE is sufficient.
e) Statements (1) and (2) TOGETHER are NOT sufficient.

The original solution is C.

But the solution does not take into account the case: 0<x<1.
If we take this case, the answer should be E.
jnelson0612
ManhattanGMAT Staff
 
Posts: 2664
Joined: Fri Feb 05, 2010 10:57 am
 

Re: Absolute Greater than Square

by jnelson0612 Mon Oct 08, 2012 1:14 pm

praks.g Wrote:Is x*|y| > y^2?

(1) x > y

(2) y > 0

a) Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
b) Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
c) Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
d) EACH statement ALONE is sufficient.
e) Statements (1) and (2) TOGETHER are NOT sufficient.

The original solution is C.

But the solution does not take into account the case: 0<x<1.
If we take this case, the answer should be E.


Be careful! Let's use an x that is between 0 and 1. Let's use 1/2. If we use the statements together, y is positive but less than x. Thus, let's say y is 1/4. Is 1/2 * 1/4 > (1/4)^2? Yes it is.

Because of this, you get the same answer whether you use an x and y between 0 and 1, an x above 1 and a y between 0 and 1, and an x and y both above above 1, as long as you follow all the constraints. Thus, the answer is C.
Jamie Nelson
ManhattanGMAT Instructor