Absolute value

This topic has expert replies
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pm
Location: Toronto
Thanked: 1710 times
Followed by:614 members
GMAT Score:800

by Stuart@KaplanGMAT » Thu Apr 23, 2009 2:44 pm
maihuna wrote:1. x^2 < 1 for -1<x<1 => |x| <1 Suff

2. |x| < 1/x
trick here is we dont know sign of x but we do know the sign of |x|
However, since we know that |x| must be positive (since x&#8800;0), we can deduce that x is positive as well.

Let's just replace |x| with +

1/x > +

well, if 1/x is greater than a positive number, 1/x must be positive, which means that x is also positive.

Now that we know that x is positive, we can multiply both sides by x to get:

x^2 < 1

and, if x^2 < 1 AND x > 0, we know that x must be a positive fraction.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3380
Joined: Mon Mar 03, 2008 1:20 am
Thanked: 2256 times
Followed by:1535 members
GMAT Score:800

by lunarpower » Wed May 13, 2009 2:36 am
iamcste wrote:Also, Stmt 2 is satisied only between 0 and 1 and NOT between -1 and 1, as you conclude.
let's keep this simple.

you can, and should, solve EVERY data sufficiency question by\
* PRETENDING THAT THE WORD "IF" PRECEDES THE NUMBERED STATEMENTS 1 AND 2, and
* PRETENDING THAT THE WORD "THEN" PRECEDES THE PROMPT QUESTION.


so, this becomes

"IF 0 < x < 1, THEN does -1 < x < 1?"

the answer to this question is an unequivocal YES, so this statement alone is sufficient.

you'll find that this "if/then approach" will take a lot of the mystery out of data sufficiency problems.
Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

--

Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron

User avatar
Master | Next Rank: 500 Posts
Posts: 229
Joined: Tue Jan 13, 2009 6:56 am
Thanked: 8 times
GMAT Score:700

by Uri » Wed Aug 12, 2009 12:33 am
thank you for simplifying the problem.