Inequality

This topic has expert replies
Source: — Problem Solving |

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 » Sun Aug 23, 2015 3:36 am
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

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pm
Location: Palo Alto, CA
Thanked: 2867 times
Followed by:511 members
GMAT Score:800

by [email protected] » Sun Aug 23, 2015 9:55 am
Hi tapanmittal,

This question can be solved by TESTing VALUES.

We're told that X/|X| < X. We're asked which of the following MUST be true?

Let's see what happens when we TEST different values for X....

IF...X = 1
1/|1| < 1 which is NOT correct. Thus, X CANNOT = 1.

IF...X = 2
2/|2| < 2 which IS correct. Thus, X CAN = 2.

With these first two TESTs, we can eliminate Answers C and D.

Given the absolute value sign, we should also consider NEGATIVE possibilities...

IF...X = -2
-2/|-2| < -2 which is NOT correct. Thus, X CANNOT = -2.

IF...X = -1/2
(-1/2)/|-1/2| < -1/2 which IS correct. Thus, X CAN = -1/2.

With these two TESTs, we can eliminate Answers A and E.

Final Answer: B

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image

GMAT Instructor
Posts: 2630
Joined: Wed Sep 12, 2012 3:32 pm
Location: East Bay all the way
Thanked: 625 times
Followed by:119 members
GMAT Score:780

by Matt@VeritasPrep » Sun Aug 23, 2015 11:08 am
Since |x| can never be negative, it's safe to multiply both sides of the inequality by |x|.

This gives us

x < x * |x|

Now we have two cases.

Case I:: x > 0

In this case, we divide both sides by x, and we get

1 < |x|

Case II:: x < 0

In this case, we divide both sides by x again, but this time the sign FLIPS, since we're dividing by a negative.

1 > |x|

Remember that x is a negative number. If x is negative, |x| = -x. So we REALLY have

1 > -x

or

-1 < x

Since x is negative, we can write this as -1 < x < 0, and we're done!

So our solution sets are

x > 1
and
0 > x > -1

The only answer that describes both sets is B. (Note that we can't have 1 ≥ x ≥ 0, but B doesn't say that we do; it only says that x, whatever it is, must be greater than -1 - it doesn't say that x can take any value greater than -1.)