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 →

Quant review (OG) Prob

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Junior | Next Rank: 30 Posts
Posts: 16
Joined: Sun Jul 27, 2008 9:45 pm
Thanked: 2 times

Re: Quant review (OG) Prob

by aspire750 » Tue Aug 12, 2008 10:52 pm
amitansu wrote:The q is : If xy>0, does (x-1)(y-1)=1 ?

1) x+y=xy
2) x=y

Stem 1 is sufficient and i agree with that.

How about stem 2 ?

Amit
xy-(x+y)+1=1

Stm1. x+y=xy so, the given eqn holds correct Sufficient

Stm2. x=y, The eqn will be
x^2-2x+1=1--> (x-1)^2=1
or
y^2-2y+1=1--> (y-1)^2=1

Insufficient to satisfy the equation
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 294
Joined: Tue Feb 26, 2008 9:05 pmFollowed by: 1 member
Thanked: 13 times

Re: Quant review (OG) Prob

by amitansu » Tue Aug 12, 2008 11:56 pm
aspire750 wrote:
amitansu wrote:The q is : If xy>0, does (x-1)(y-1
xy-(x+y)+1=1

Stm1. x+y=xy so, the given eqn holds correct Sufficient

Stm2. x=y, The eqn will be
x^2-2x+1=1--> (x-1)^2=1
or
y^2-2y+1=1--> (y-1)^2=1

Insufficient to satisfy the equation
Ok.

from 2 : x-1=+ or - 1
and y-1=+ or -1

so, x is either 2 or 0 and y is also either 2 or 0
since it is given xy>0 , x and y have to be either
+ve or -ve at the same time.

So, x and y could be 2 each since they can't be 0 to be > 0.

Amit
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 30
Joined: Fri Nov 23, 2007 9:04 am
Thanked: 1 times

by varmaskarma » Wed Aug 13, 2008 5:43 am
what is the ans?

for 2:

(x-1)(y-1)=1
xy-x-y+1 = 1
=> xy-x-y=0

if x=y

=> x^2 -x -x = 0

=> x^2 = 2x

=> x=2 i.e. y=2 ( as x=y)

therfore (x-1)(y-1) = 1....................sufficient
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 48
Joined: Fri Aug 08, 2008 4:44 am
Thanked: 4 times
GMAT Score:750

by santa_dem » Wed Aug 13, 2008 5:52 am
It doesn't ask if you can solve the problem, it says:

is (x-1)(y-1)=1

1. is obvios

2. Well, x=y.

But if x=y=8, then 7*7=49<>1, so 2 is not sufficient to prove that (x-1)(y-1)=1. It can be solved to x=2, but that's not what we are asked now, is it?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 294
Joined: Tue Feb 26, 2008 9:05 pmFollowed by: 1 member
Thanked: 13 times

by amitansu » Wed Aug 13, 2008 9:31 am
varmaskarma wrote:what is the ans?

for 2:

(x-1)(y-1)=1
xy-x-y+1 = 1
=> xy-x-y=0

if x=y

=> x^2 -x -x = 0

=> x^2 = 2x

=> x=2 i.e. y=2 ( as x=y)

therfore (x-1)(y-1) = 1....................sufficient

The ans is : step 2 is insufficient .
OG solution says it can't find a unique value of x aor y.
I couldn't convince myself for that...

BUt yes, as santa_dem says, the value of x and y could be anything be it's 2 or 8 or whatever....the ans could be yes and no also.so not sufficient.To me this is more convincing.

Thank you all.

Amit
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 343
Joined: Mon Jan 21, 2008 3:28 pm
Thanked: 4 times

by arorag » Thu Aug 14, 2008 9:10 pm
OG is correct see below
If x=y then stat 2
IF (x-1)^2= X^2-2X+1= 1
X^2-2X=0
x=2 OR x=0
buT if x=2 then xy=0 contradictory from info given
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1