BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

DS

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 33
Joined: Mon Aug 04, 2008 6:52 am
Thanked: 2 times

by bomond » Thu Aug 28, 2008 11:45 am
There is one way if you want. But it's a bit odd.

ST 1. In order to avoid model square(sorry can't express) the both sides
(x+1)^2=(2(x-1))^2
x^2+2x+1=4x^2-8x-4
3x^2-10x-5=0
appr. x1=-1/3 x2=3.5 INSUFF

ST 2. Same way
(x-3)^2 ≠0
x ≠3 INSUFF

BOTH INSUFF

I go for E
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 172
Joined: Wed Oct 31, 2007 11:21 am
Thanked: 1 times

by gmattester » Thu Aug 28, 2008 11:50 am
No this is not odd....
This is an excellent method but I am not sure I can apply this method for every absolute value question.
I mean to say something generic which I can apply to all absolute questions
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members
Location: Toronto
Thanked: 1710 times
GMAT Score:800

by Stuart@KaplanGMAT » Thu Aug 28, 2008 12:08 pm
bomond wrote:There is one way if you want. But it's a bit odd.

ST 1. In order to avoid model square(sorry can't express) the both sides
(x+1)^2=(2(x-1))^2
x^2+2x+1=4x^2-8x-4
Math is a bit off:

(x+1)^2=(2(x-1))^2
x^2 + 2x + 1 = (2x - 2)^2
x^2 + 2x + 1 = 4(x^2) - 8x + 4
0 = 3(x^2) - 10x + 3
0 = (3x - 1) (x - 3)
3x = 1 or x = 3
x = 1/3 or x = 3

x may or may not be between -1 and +1.. insufficient.

However, when we combine with:

(2) x ≠ 3

we know that the only possible value of x is 1/3, so choose (c): together the statements are sufficient.

In fact, (c) is a great strategic guess on this question, long before doing all the math.

Statement (2) seems pretty random, so either we're being given a totally useless piece of information or x ≠ 3 will eliminate a possibility from (1). As soon as we see that (1) can be turned into a quadratic, we should anticipate that (1) will give us two values for x (so will be insufficient) and (2) will narrow it down to just one possibility.

The better you know the GMAT, the less work you'll need to do to confidently pick up points. Knowing how and when to guess strategically is a huge advantage on test day.

To go back to the original poster's question, yes, squaring both sides of an absolute value equation is often a great approach to these questions.
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
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members
Location: Montreal
Thanked: 1090 times
GMAT Score:780

Re: DS

by Ian Stewart » Thu Aug 28, 2008 2:18 pm
gmattester wrote:Is lxl< 1?
(1) lx + 1l = 2lx - 1l
(2) lx - 3l &#8800; 0

Besides plugging values, can someone tell me another method how to solve absolute values questions.
There is another way, which I use on pretty much every absolute value GMAT question, but you'd want to practice it a bit before beginning to use it on a test. Remember that |x| is the distance between x and zero on the number line, and |x-y| is the distance between x and y on the number line. If you understand these two facts, you can change many problems about absolute value into problems about distances on the number line, and you can bypass the algebra altogether. Doing that here:

Is |x| < 1? --> Is x less than 1 away from zero?

1) lx + 1l = 2lx - 1l ---> lx - (-1)l = 2lx - 1l

In words this says "the distance between x and -1 is twice the distance between x and 1", or phrased more simply, "x is twice as far from -1 as x is from 1". If you draw a number line, you'll see there are two places x could be: between -1 and 1 (but closer to 1), or to the right of 1. It's not difficult to see that x = 3 is one of the two solutions. Insufficient.

2) tells us x is not 3. Insufficient.

Together, there is only one possible solution, the point between -1 and 1, so the answer is yes, |x| < 1, and the two statements are sufficient together. C.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 33
Joined: Mon Aug 04, 2008 6:52 am
Thanked: 2 times

by bomond » Fri Aug 29, 2008 5:59 am
I'm sorry gmattester. I made a calculation mistake. Thanks to Stuart, I got it.

Ian Stewart! Do you think your method is always helpful

How do you approach to this problem: |x-1|=|2x+3| (instead lx + 1l = 2lx - 1l)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1