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

It is currently 25 Oct 2014, 04:29

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

m04 #24

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
avatar
Joined: 22 Sep 2008
Posts: 11
Followers: 0

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

m04 #24 [#permalink] New post 09 Oct 2008, 14:47
Is x = 0 ?

1. xy = x
2. x + y = y

[Reveal] Spoiler: OA
B

Source: GMAT Club Tests - hardest GMAT questions

Please explain why statement 1 is insufficient.
_________________

It's not the IMO, it's the OA!!

Kaplan GMAT Prep Discount CodesKnewton GMAT Discount CodesManhattan GMAT Discount Codes
1 KUDOS received
VP
VP
User avatar
Joined: 30 Jun 2008
Posts: 1048
Followers: 11

Kudos [?]: 291 [1] , given: 1

Re: m04 #24 [#permalink] New post 09 Oct 2008, 18:26
1
This post received
KUDOS
gmat4life wrote:
Is x=0?

1. xy=x

2. x+y=y

Please explain why statement 1 is insufficient.


Now xy=x means xy-x=0 or x(1-y)=0
For the equation x(1-y)=0 to hold good, either x has to be 0 or y has to be 1. It can very well be that x=0 and y=1 at the same time. We are not sure. So since it is not clear if x=0 or not, this statement is not sufficient.

Now in statement 2. x+y=y clearly shows x=0.

So it must be B

HTH
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Check out my GMAT blog - GMAT Tips and Strategies

1 KUDOS received
Darden Thread Master
User avatar
Joined: 04 Oct 2010
Posts: 60
GMAT 1: 720 Q48 V41
Followers: 3

Kudos [?]: 19 [1] , given: 17

Re: m04 #24 [#permalink] New post 16 Oct 2010, 23:07
1
This post received
KUDOS
for statement 1 :
x*y=x
if x=0 and y=1 then 0*1=0 ; satisfies
if x=2 and y=1 then 2*1=2 ; satisfies

thus statement 1 is insufficient to say that x is 0

for statement 2:
x+y=y
if x=0 and y=any integer then 0+y = y ; satisfies
if x=2(or any int but not zero) and y=any int then x+y=y is not satisfying

thus statement 2 is sufficient to say that x=0

SO B

But what would be the answer if the second statement was : x + y = x ??
_________________

---
Jimmy

Life`s battles dont always go,
To the stronger or faster man;
But sooner or later the man who wins,
Is the man who THINKS HE CAN .


KUDOS me if you feel my contribution has helped you.

Expert Post
1 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23409
Followers: 3614

Kudos [?]: 28941 [1] , given: 2874

Re: m04 #24 [#permalink] New post 20 Oct 2010, 04:16
1
This post received
KUDOS
Expert's post
sivai87 wrote:
@ GMAT BULL

Is X = 0?

1) X * Y = X

2) X + Y = X

The statements 1 and 2 are contradicting to each other..
Option 1 says that, X * Y = X which tends to give Y = 1,

But option 2 gives, X + Y = X, and So Y = 0.
I believe such questions wont appear in GMAT and so less to worry about this question... :)


Not so. First of all statement (2) is x+y=y and not x+y=x.

Next, (1) xy=x --> x(y-1)=0 --> either x=0 (and y can take any value) OR y=1 (and x can take any value). So we can not say that y=1 from this statement.

If the question were:

Is x = 0?

(1) xy = x
(2) x+y=x (Note that this statement is changed)

Then the answer would be C:

(1) xy=x --> x(y-1)=0 --> either x=0 (and y can take any value) OR y=1 (and x can take any value). Not sufficient.
(2) x+y=x --> y=0. Not sufficient to answer whether x=0.

(1)+(2) As from (2) y=0\neq{1} then according to (1) x=0. Sufficient.

So for this revised question answer would be C.

Hope it helps.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

CIO
CIO
avatar
Joined: 02 Oct 2007
Posts: 1218
Followers: 87

Kudos [?]: 691 [0], given: 334

GMAT ToolKit User
Re: m04 #24 [#permalink] New post 22 Oct 2008, 06:04
Thanks for a good explanation!
+1
amitdgr wrote:
gmat4life wrote:
Is x=0?

1. xy=x

2. x+y=y

Please explain why statement 1 is insufficient.


Now xy=x means xy-x=0 or x(1-y)=0
For the equation x(1-y)=0 to hold good, either x has to be 0 or y has to be 1. It can very well be that x=0 and y=1 at the same time. We are not sure. So since it is not clear if x=0 or not, this statement is not sufficient.

Now in statement 2. x+y=y clearly shows x=0.

So it must be B

HTH

_________________

Welcome to GMAT Club! :)
Facebook TwitterGoogle+LinkedIn
Want to solve GMAT questions on the go? GMAT Club iPhone app will help.
Please read this before posting in GMAT Club Tests forum
Result correlation between real GMAT and GMAT Club Tests
Are GMAT Club Test sets ordered in any way?

Take 15 free tests with questions from GMAT Club, Knewton, Manhattan GMAT, and Veritas.

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Intern
Intern
avatar
Affiliations: SPE
Joined: 02 Sep 2010
Posts: 9
Location: Copenhagen
Schools: Columbia, MIT, Harvard, LBS
Followers: 0

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

Re: m04 #24 [#permalink] New post 15 Oct 2010, 05:02
This question goes to show that when you have been looking at 700 level questions too long, you try and pick holes in something as simple as x = y - y ....

on the other hand, its good to finally get a question right!
Intern
Intern
avatar
Joined: 10 Oct 2010
Posts: 7
Followers: 0

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

Re: m04 #24 [#permalink] New post 15 Oct 2010, 08:36
For the first option, lets assume Y = 1. So whatever the value of x, the product of XY is always X.

X * 1 = X (For any values of X). So, option 1 is ruled out..
Director
Director
avatar
Joined: 21 Dec 2009
Posts: 589
Concentration: Entrepreneurship, Finance
Followers: 15

Kudos [?]: 292 [0], given: 20

Re: m04 #24 [#permalink] New post 18 Oct 2010, 04:48
Hi Jimmy86;
if (2) where: x + y = x
--> y = 0 [no information about x after subtracting x from both sides]

combining (1) & (2) [x*y=x; x+y=x]:
x(0) = x
for all values of x, x*0 is always a zero.
So, we can say x (the result of the multiplication) is a zero.
IMO C
_________________

KUDOS me if you feel my contribution has helped you.

Intern
Intern
avatar
Joined: 10 Oct 2010
Posts: 7
Followers: 0

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

Re: m04 #24 [#permalink] New post 18 Oct 2010, 05:20
If X+Y=X, then I go for E..

we have options,

x * y = x and

x + y = x.

Combining 1 and 2,

(x + y) * y = x,

xy + y^2 = x

y (x + y) = x and so, x will be zero only if Y is also 0 or else the condition is not satisfied. So, IMO its E. :)


jimmy86 wrote:
for statement 1 :
x*y=x
if x=0 and y=1 then 0*1=0 ; satisfies
if x=2 and y=1 then 2*1=2 ; satisfies

thus statement 1 is insufficient to say that x is 0

for statement 2:
x+y=y
if x=0 and y=any integer then 0+y = y ; satisfies
if x=2(or any int but not zero) and y=any int then x+y=y is not satisfying

thus statement 2 is sufficient to say that x=0

SO B

But what would be the answer if the second statement was : x + y = x ??
Darden Thread Master
User avatar
Joined: 04 Oct 2010
Posts: 60
GMAT 1: 720 Q48 V41
Followers: 3

Kudos [?]: 19 [0], given: 17

Re: m04 #24 [#permalink] New post 18 Oct 2010, 06:06
[quote="sivai87"]If X+Y=X, then I go for E..

we have options,

x * y = x and

x + y = x.

Combining 1 and 2,

(x + y) * y = x,

xy + y^2 = x

y (x + y) = x and so, x will be zero only if Y is also 0 or else the condition is not satisfied. So, IMO its E. :)




I agree... its E.

in case statement 2 : x+y = x
x=-1 , y=0 gives -1+0 = -1 ; satisfies
x=0 , y= 0 gives 0+0 = 0 ; satisfies
we see x is not necessarily 0. Insufficient

And combining
y(x+y)=x
if x=0 ; y=0 then 0*(0+0)=0 ; satisfies
if x=1/2 ; y=1/2 then 1/2*(1/2+1/2)=1/2 ; satisfies
So x is not necessarily 0.Insufficient

Thus IMO its E

But what if the question states that x is an integer.
Then i suppose the only value that of x that satisfies y(x+y)=x is x=0. and answer would be C(not sure, feel i am missing something)
_________________

---
Jimmy

Life`s battles dont always go,
To the stronger or faster man;
But sooner or later the man who wins,
Is the man who THINKS HE CAN .


KUDOS me if you feel my contribution has helped you.

Intern
Intern
User avatar
Status: Current Student
Joined: 16 May 2010
Posts: 44
Schools: Darden '13
Followers: 0

Kudos [?]: 8 [0], given: 4

Re: m04 #24 [#permalink] New post 18 Oct 2010, 07:05
Supasubi wrote:
This question goes to show that when you have been looking at 700 level questions too long, you try and pick holes in something as simple as x = y - y ....

on the other hand, its good to finally get a question right!


Haha yes! I definitely know what you mean. You're so traumatized from every question trying to trick you, that you're reluctant to believe that the answer could be sufficient with something as easy as X=Y-Y. I stared at it for a good 30 seconds trying to pick it apart too. That's hilarious.
Director
Director
avatar
Joined: 21 Dec 2009
Posts: 589
Concentration: Entrepreneurship, Finance
Followers: 15

Kudos [?]: 292 [0], given: 20

Re: m04 #24 [#permalink] New post 18 Oct 2010, 08:30
(2) if y = x - x, then, it is sufficient to say y = "0".

plug in y (0) into (1) [x*y = x]
or x = x*y
x = x*0
RHS = x*0 = 0
for any value of a number, 0 times that number = 0
So, RHS is always "0"
LHS = x
LHS = RHS
--> x = RHS
x = 0
Sufficient

So, C IMO....except am doing something stupid somewhere.
Please correct me.
_________________

KUDOS me if you feel my contribution has helped you.

Intern
Intern
avatar
Joined: 10 Oct 2010
Posts: 7
Followers: 0

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

Re: m04 #24 [#permalink] New post 18 Oct 2010, 09:48
@Gmatbull..

Buddy, I dont think u went wrong... I believe I am somewhere wrong..

The first mistake i made was, in substitution...
I shud have substituted as (x+y) * y = (x+y)... instead of (X+Y)*Y= X..

But even after this I am getting (X+Y)*Y=(X+Y) ---> Y=1.. and this will finally yield that Both option are not suffiient...
And I am not sure how to proceed further...

Can anyone help me pls...

gmatbull wrote:
(2) if y = x - x, then, it is sufficient to say y = "0".

plug in y (0) into (1) [x*y = x]
or x = x*y
x = x*0
RHS = x*0 = 0
for any value of a number, 0 times that number = 0
So, RHS is always "0"
LHS = x
LHS = RHS
--> x = RHS
x = 0
Sufficient

So, C IMO....except am doing something stupid somewhere.
Please correct me.
Director
Director
avatar
Joined: 21 Dec 2009
Posts: 589
Concentration: Entrepreneurship, Finance
Followers: 15

Kudos [?]: 292 [0], given: 20

Re: m04 #24 [#permalink] New post 18 Oct 2010, 11:19
sivai87 wrote:
@Gmatbull..
The first mistake i made was, in substitution...
I shud have substituted as (x+y) * y = (x+y)... instead of (X+Y)*Y= X..

But even after this I am getting (X+Y)*Y=(X+Y) ---> Y=1.. and this will finally yield that Both option are not suffiient...
And I am not sure how to proceed further...

I think you seem to make the expression difficult to yourself.
First, realize that (2) has simplified the job:
from x+y = x, you know y = 0.
(x+y) * y = (x+y) ==> (x+y)0 = x+0
0 = x +0
0 = x
you still arrive at C.
_________________

KUDOS me if you feel my contribution has helped you.

Intern
Intern
avatar
Joined: 10 Oct 2010
Posts: 7
Followers: 0

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

Re: m04 #24 [#permalink] New post 20 Oct 2010, 03:54
@ GMAT BULL

Is X = 0?

1) X * Y = X

2) X + Y = X

The statements 1 and 2 are contradicting to each other..
Option 1 says that, X * Y = X which tends to give Y = 1,

But option 2 gives, X + Y = X, and So Y = 0.
I believe such questions wont appear in GMAT and so less to worry about this question... :)

gmatbull wrote:
sivai87 wrote:
@Gmatbull..
The first mistake i made was, in substitution...
I shud have substituted as (x+y) * y = (x+y)... instead of (X+Y)*Y= X..

But even after this I am getting (X+Y)*Y=(X+Y) ---> Y=1.. and this will finally yield that Both option are not suffiient...
And I am not sure how to proceed further...

I think you seem to make the expression difficult to yourself.
First, realize that (2) has simplified the job:
from x+y = x, you know y = 0.
(x+y) * y = (x+y) ==> (x+y)0 = x+0
0 = x +0
0 = x
you still arrive at C.
Manager
Manager
avatar
Joined: 10 Jan 2011
Posts: 244
Location: India
GMAT Date: 07-16-2012
GPA: 3.4
WE: Consulting (Consulting)
Followers: 0

Kudos [?]: 21 [0], given: 25

Reviews Badge
Re: m04 #24 [#permalink] New post 19 Oct 2011, 08:14
answer is B
statement 1 XY=X means y=1 but X can take any value not sufficient
statement 2 x + y = Y means X = y-y or X=0 sufficient
_________________

-------Analyze why option A in SC wrong-------

Intern
Intern
avatar
Joined: 17 Aug 2011
Posts: 2
Followers: 3

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

Re: m04 #24 [#permalink] New post 19 Oct 2011, 11:51
Bunuel wrote:
sivai87 wrote:
@ GMAT BULL

Is X = 0?

1) X * Y = X

2) X + Y = X

The statements 1 and 2 are contradicting to each other..
Option 1 says that, X * Y = X which tends to give Y = 1,

But option 2 gives, X + Y = X, and So Y = 0.
I believe such questions wont appear in GMAT and so less to worry about this question... :)


Not so. First of all statement (2) is x+y=y and not x+y=x.

Next, (1) xy=x --> x(y-1)=0 --> either x=0 (and y can take any value) OR y=1 (and x can take any value). So we can not say that y=1 from this statement.

If the question were:

Is x = 0?

(1) xy = x
(2) x+y=x (Note that this statement is changed)

Then the answer would be C:

(1) xy=x --> x(y-1)=0 --> either x=0 (and y can take any value) OR y=1 (and x can take any value). Not sufficient.
(2) x+y=x --> y=0. Not sufficient to answer whether x=0.

(1)+(2) As from (2) y=0\neq{1} then according to (1) x=0. Sufficient.

So for this revised question answer would be C.

Hope it helps.



I seem to recall that you can't add/subtract variables from both sides of the equation unless you know the sign of the variables. But the question doesn't tell you the sign of x or y so I don't think the problem can be approached this way. I think the only way to answer the question is to plug in numbers for x and y then check to see if the equation holds.
Manager
Manager
avatar
Joined: 20 Nov 2010
Posts: 227
Followers: 4

Kudos [?]: 7 [0], given: 38

Re: m04 #24 [#permalink] New post 19 Oct 2011, 12:32
St 1:
xy = x. Either x=0 and y can take any value OR x can be any value and y=1. So insufficient.

St2
x+y = Y => X=0, Y can be anything. Hence Sufficient.

OA is B.
_________________

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MGMAT 6 650 (51,31) on 31/8/11
MGMAT 1 670 (48,33) on 04/9/11
MGMAT 2 670 (47,34) on 07/9/11
MGMAT 3 680 (47,35) on 18/9/11
GMAT Prep1 680 ( 50, 31) on 10/11/11

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CR notes
http://gmatclub.com/forum/massive-collection-of-verbal-questions-sc-rc-and-cr-106195.html#p832142
http://gmatclub.com/forum/1001-ds-questions-file-106193.html#p832133
http://gmatclub.com/forum/gmat-prep-critical-reasoning-collection-106783.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html?hilit=chineseburned

Current Student
User avatar
Joined: 16 Sep 2010
Posts: 227
Location: United States
Concentration: Finance, Real Estate
GMAT 1: 740 Q48 V42
Followers: 7

Kudos [?]: 61 [0], given: 2

Re: m04 #24 [#permalink] New post 20 Nov 2011, 06:44
B.

1 tells us that y=1 and 2 tells us that x=0.
Manager
Manager
avatar
Joined: 06 May 2012
Posts: 77
Followers: 2

Kudos [?]: 16 [0], given: 16

Re: m04 #24 [#permalink] New post 07 Oct 2012, 11:47
Quote:
Is x = 0 ?

1. xy = x
2. x + y = y


For Option1, which of the below method need to be followed?

Method1 ---- xy = x ----> xy-x = 0 ----> x(y-1) = 0 ----> x = 0, y = 1 ---- I thought this method is always true in determining a value
Method2 ---- xy = x - Substitute values x=0 & ycan be any value? or x can be any value and y=1?
Re: m04 #24   [#permalink] 07 Oct 2012, 11:47
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic M04-24 Bunuel 3 15 Sep 2014, 23:23
m04 bibha 1 12 Jul 2010, 03:49
M04 #24 gmat00 1 04 May 2010, 15:16
m04q24 shachidubey 1 07 Sep 2009, 11:05
m04 #24 gmat4life 2 09 Oct 2008, 17:18
Display posts from previous: Sort by

m04 #24

  Question banks Downloads My Bookmarks Reviews Important topics  

Go to page    1   2    Next  [ 25 posts ] 

Moderators: WoundedTiger, Bunuel



GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.