Target Test Prep's 2024 GMAT Focus Edition prep is discounted for the BTG community!

Redeem
Target Test Prep
5-Day Free Trial
5-day free, full-access trial TTP

Available with Beat the GMAT members only code

MORE DETAILS
Target Test Prep
Magoosh
Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

MORE DETAILS
Magoosh

xy=1

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Mon May 26, 2008 4:12 pm

xy=1

by ch0719 » Sat Jan 03, 2009 7:14 pm
if xy=1, what is the value of [2(x+y)^2]/[2(x-y)^2]?

2
4
8
16
32


OA is 16

I tried to plug in numbers but that doesn't work
:?
Top
Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Sat Jan 03, 2009 7:18 pm
Question should read(I think its been posted before)

2^(x+y)^2 / 2^(x-y)^2

2 ^ (x^2+y^2+2xy) / 2^(x^+y^2-2xy) (a^m / a^n = a^(m-n))

2 ^(x^2+y^2+2xy-x^2-y^2+2xy)

2^(4xy)

2^4

16
Top
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Mon May 26, 2008 4:12 pm

by ch0719 » Sat Jan 03, 2009 7:26 pm
this is the original question captured img
Attachments
gmattemp1.jpg
Top
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Mon May 26, 2008 4:12 pm

by ch0719 » Sat Jan 03, 2009 7:28 pm
could that be a type error from the prep software? :shock:
Top
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pm
Thanked: 237 times
Followed by:25 members
GMAT Score:730

by logitech » Sat Jan 03, 2009 7:29 pm
so plugging numbers are useful in these question types in which you have no limitations for your X and Y

XY=1 means : X=1 and Y=1

So , the question turns into 2^4/1 = 16

That's it!
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Sat Jan 03, 2009 7:52 pm
Hmm, the question as it stands couldn't be a GMAT question.
To begin, there would have been a proviso that rules out the possibility of the denominator = 0 (e.g., x cannot equal y)
Also, the value of this rational expression varies as we plug in different values for x and y such that xy=1.
Where did you find this question?
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Sat Jan 03, 2009 8:00 pm
XY=1 means : X=1 and Y=1
x=-1 y=-1 also possible(in general) but I guess it doesnt make a difference for this problem

x=2 y=1/2

x=3 y=1/3

....... So on
Top
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pm
Thanked: 237 times
Followed by:25 members
GMAT Score:730

by logitech » Sat Jan 03, 2009 8:10 pm
Brent Hanneson wrote:Hmm, the question as it stands couldn't be a GMAT question.
To begin, there would have been a proviso that rules out the possibility of the denominator = 0 (e.g., x cannot equal y)
Also, the value of this rational expression varies as we plug in different values for x and y such that xy=1.
Where did you find this question?
X can be equal to Y and this gives us 2^0=1

Cramya,

How about 4 x 1/4 :D

X=Y=1 is an example that requires the less work.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Mon May 26, 2008 4:12 pm

by ch0719 » Sat Jan 03, 2009 8:32 pm
Brent Hanneson wrote:Hmm, the question as it stands couldn't be a GMAT question.
To begin, there would have been a proviso that rules out the possibility of the denominator = 0 (e.g., x cannot equal y)
Also, the value of this rational expression varies as we plug in different values for x and y such that xy=1.
Where did you find this question?
I found this on the OG prep software, its in CAT 1. This is prob not the latest version because I am using my old computer and I installed the gmat prep on this computer quite a while ago.
Top
Senior | Next Rank: 100 Posts
Posts: 87
Joined: Tue Dec 23, 2008 11:06 pm
Thanked: 2 times

by rajataga » Sun Jan 04, 2009 2:55 am
logitech wrote:
Brent Hanneson wrote:Hmm, the question as it stands couldn't be a GMAT question.
To begin, there would have been a proviso that rules out the possibility of the denominator = 0 (e.g., x cannot equal y)
Also, the value of this rational expression varies as we plug in different values for x and y such that xy=1.
Where did you find this question?
X can be equal to Y and this gives us 2^0=1

Cramya,

How about 4 x 1/4 :D

X=Y=1 is an example that requires the less work.

The denominator would be 0 if the X and Y are equal, since it's not 2^0, but 2 X 0....
Top
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pm
Thanked: 237 times
Followed by:25 members
GMAT Score:730

by logitech » Sun Jan 04, 2009 11:26 am
rajataga wrote:

The denominator would be 0 if the X and Y are equal, since it's not 2^0, but 2 X 0....
My poor old eyes :) Thanks!
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Post new topic Post Reply
• Page 1 of 1