Is xy < 1?

This topic has expert replies
Moderator
Posts: 2058
Joined: Sun Oct 29, 2017 4:24 am
Thanked: 1 times
Followed by:5 members

Is xy < 1?

by M7MBA » Sat Nov 25, 2017 8:32 am
Is xy < 1?

(1) 2/x > 3y
(2) x > 0

The OA is C .

I need some help here. Can you experts explain to me how to solve this DS question?
Source: — Data Sufficiency |

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sat Nov 25, 2017 10:23 am
M7MBA wrote:Is xy < 1?

(1) 2/x > 3y
(2) x > 0
Statement 1:
Let y=-1, implying that 2/x > -3.
Case 1: x=-1, with the result that 2/x = 2/(-1) = -2
In this case, xy = (-1)(-1) = 1, so the answer to the question stem is NO.
Case 2: x=1, with the result that 2/x = 2/1 = 2
In this case, xy = (1)(-1) = -1, so the answer to the question stem is YES.
Since the answer is NO in Case 1 but YES in Case 2, INSUFFICIENT.

Statement 2:
If x=1 and y=1, then xy = 1*1 = 1, with the result that the answer to the question stem is NO.
If x=1 and y=0, then xy = 1*0 = 0, with the result that the answer to the question stem is YES.
Since the answer is NO in the first case but YES in the second case, INSUFFICIENT.

Statements combined:
Since x>0, both sides of 2/x > 3y can safely be multiplied by x:
x(2/x) > 3y(x)
2 > 3xy
2/3 > xy
xy < 2/3.
Thus, the answer to the question stem is YES.
SUFFICIENT.

The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3