Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 02 Jul 2015, 16:21

### 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

# Does xy=x^2 ?

Author Message
TAGS:
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

Does xy=x^2 ? [#permalink]  09 Jan 2004, 16:44
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Again, I disagree with the OA provided for a question. This one is taken from the 3rd CAT of the PR CD.

Does xy=x^2 ?

(1) xy=y^2
(2) x^2=y^2
Manager
Joined: 26 Dec 2003
Posts: 227
Location: India
Followers: 1

Kudos [?]: 2 [0], given: 0

Martin is it C by combining both the statements we can say that xy=y^2
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

rakesh1239 wrote:
Martin is it C by combining both the statements we can say that xy=y^2

Answer is C but I get D. Could you tell me what I'm doing wrong?

(1) xy=y^2 then x=y^2/y then x=y so xx=x^2 suff.

If xy=x^2 then x^2*y^2=x^4

(2) x^2=y^2 substitute above then you get x^2*x^2=x^4
Manager
Joined: 26 Dec 2003
Posts: 227
Location: India
Followers: 1

Kudos [?]: 2 [0], given: 0

substitute the value of statement 1 in 2 or statement 2 in 1, we can cancel out y^2 and say that xy=x^2
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

rakesh1239 wrote:
substitute the value of statement 1 in 2 or statement 2 in 1, we can cancel out y^2 and say that xy=x^2

Yeah, I know. I was showing you a way in which each statement by itself is sufficient. If my reasoning is correct then answer should be D instead of C. (D beats C in DS)

Do you see anything wrong in my last post?
Manager
Joined: 26 Dec 2003
Posts: 227
Location: India
Followers: 1

Kudos [?]: 2 [0], given: 0

in the first statement u derived x=y^2/y , cancelled y with y and said x=y but y can be -ve too, in which case x= -y
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

rakesh1239 wrote:
in the first statement u derived x=y^2/y , cancelled y with y and said x=y but y can be -ve too, in which case x= -y

But x could no be -y , suppose x=2 and y=-2

then if x*y=y*y we would get 2*(-2)=(-2)*(-2) => -4=4 not possible
Manager
Joined: 26 Dec 2003
Posts: 227
Location: India
Followers: 1

Kudos [?]: 2 [0], given: 0

that was what i was saying that in ur case in the 1st statement u r getting x= -y which cant be and so we need to combine both the statements
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

I still don't see how I could get x=-y

All I said was that if we have X*Y=Y*Y then X=Y
Intern
Joined: 01 Dec 2003
Posts: 35
Location: infront of my LCD
Followers: 0

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

Hmmm...i get A

Does xy=xx

For statement 1: xy has to be + since yy is + and xy=yy so either x=y or -x=-y will work.

For statement 2: we agree that x=-1 and y=1 will work since xx & yy will be positive so it doesnt matter what the sign for x or y is but it will for the stem xy=xx

I'm lost...can any explain...or show me my error?
Senior Manager
Joined: 22 May 2003
Posts: 334
Location: Uruguay
Followers: 1

Kudos [?]: 41 [0], given: 0

Anybody else wants to try this problem?

We are all getting different answers...
Director
Joined: 28 Oct 2003
Posts: 503
Location: 55405
Followers: 1

Kudos [?]: 11 [0], given: 0

Does xy=x^2 ?

(1) xy=y^2
(2) x^2=y^2

1) consider (1,0). It makes (1) correct, but it does not make the problem correct. (1,1) on the other hand, makes both of them correct. Insufficient.

2) tells us only that the absolute value of X is the absolute value of y. not sufficient, since if x is negative and y is positive, that the equation holds, but if x is positive and y is negative, the equation does not hold. insufficient.

Senior Manager
Joined: 11 Nov 2003
Posts: 355
Location: Illinois
Followers: 1

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

Here is how it should go.

(1) xy = y^2 => y^2 - xy = 0 => y(y-x) = 0

=> y = 0 or y = x
If y = 0 then the question becomes is x^2 = 0? we do not know.

if y= x, then LHS of the question becomes x^2. so the answer is yes.

So the statement 1 insufficient

(2) x^2 = y^2

=> x^2 - y^2 = 0 => (x+y) (x-y) = 0

=> x = -y or x = y

If x = -y => y = -x, the question becomes is -x^2 = x^2, the answer is NO

If x = y then the answer to the question is YES.

sO (2) INSUFFICIENT

TOGETHER

statement (1) gives y = 0 or y = x
statement(2) gives x = -y or x = y

Similar topics Replies Last post
Similar
Topics:
3 Is 0 < (x−y)/(x−2y) < 1? 5 13 Feb 2015, 07:45
5 Does s = 5 - t ? 11 25 Oct 2012, 20:09
6 If y does not equal 0. Does x = 0 ? 6 06 Jan 2011, 05:32
DS: If X$Y=x^2 - y^2 / (x-y) then what is the value of x$y? 2 05 Oct 2007, 04:44
If x$y=x^2-y^2/(x-y), then what is the value of x$y? A) 5 25 Mar 2007, 13:33
Display posts from previous: Sort by