xy >0 does (x-1)(y-1) =1 x+y=xy x=y spoiler below the : DS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 23 Jan 2017, 03:14

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# xy >0 does (x-1)(y-1) =1 x+y=xy x=y spoiler below the

Author Message
Senior Manager
Joined: 14 Jun 2007
Posts: 399
Followers: 1

Kudos [?]: 14 [0], given: 0

xy >0 does (x-1)(y-1) =1 x+y=xy x=y spoiler below the [#permalink]

### Show Tags

07 Aug 2007, 13:40
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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

x+y=xy

x=y

spoiler below the line:

________________________________________________

so i thought that the answer was D. if x=y then we have y^2-2y+1=1

which simplifies to y(y-2)=0 so y = 0 or y = 2.

since x=y we have:

(0-1)(0-1)=1 and (2-1)(2-1)=1.

what did i miss here?
Senior Manager
Joined: 24 Nov 2006
Posts: 350
Followers: 1

Kudos [?]: 25 [0], given: 0

Re: GREEN OG DS #80 [#permalink]

### Show Tags

07 Aug 2007, 13:58
anonymousegmat wrote:
xy >0 does (x-1)(y-1) =1

x+y=xy

x=y

The question can be rewritten as: "xy - x - y = 0?"

(1) Suff.

(2) Insuff.

A.
Senior Manager
Joined: 06 Mar 2006
Posts: 492
Followers: 7

Kudos [?]: 179 [0], given: 1

Re: GREEN OG DS #80 [#permalink]

### Show Tags

07 Aug 2007, 14:00
anonymousegmat wrote:

________________________________________________

so i thought that the answer was D. if x=y then we have y^2-2y+1=1

which simplifies to y(y-2)=0 so y = 0 or y = 2.

since x=y we have:

(0-1)(0-1)=1 and (2-1)(2-1)=1.

what did i miss here?

You can not solve it the like this. From your equation, you solve it like you already assume (x-1)(y-1)=1, and of course the answer you get will be the one fit the criteria. You need to look at the ones doesn't fit as well. What about x=y=3? It does fit the description that xy>0, but in case of x=y=3 (x-1)(y-1) does not equal to 1. Therefore, insufficient.
Senior Manager
Joined: 14 Jun 2007
Posts: 399
Followers: 1

Kudos [?]: 14 [0], given: 0

Re: GREEN OG DS #80 [#permalink]

### Show Tags

07 Aug 2007, 15:40
eileen1017 wrote:
anonymousegmat wrote:

________________________________________________

so i thought that the answer was D. if x=y then we have y^2-2y+1=1

which simplifies to y(y-2)=0 so y = 0 or y = 2.

since x=y we have:

(0-1)(0-1)=1 and (2-1)(2-1)=1.

what did i miss here?

You can not solve it the like this. From your equation, you solve it like you already assume (x-1)(y-1)=1, and of course the answer you get will be the one fit the criteria. You need to look at the ones doesn't fit as well. What about x=y=3? It does fit the description that xy>0, but in case of x=y=3 (x-1)(y-1) does not equal to 1. Therefore, insufficient.

you would think that after i TYPED the question I would have noticed that... lol
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5062
Location: Singapore
Followers: 30

Kudos [?]: 358 [0], given: 0

### Show Tags

07 Aug 2007, 17:13
St1:
x+y = xy
if x = 2, y = 2, then (x-1)(y-1) = 1
Only one pair works. Sufficient.

St2:
x=y.
if x = 1, y = 1, then (x-1)(y-1) = 0
if x = 2, y = 2, then (x-1)(y-1) = 1
Insufficient.

Ans A
07 Aug 2007, 17:13
Display posts from previous: Sort by