It is currently 20 Nov 2017, 14:52

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x y and z are positive is xz = 7xy ?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Manager
Manager
avatar
B
Joined: 21 Jun 2011
Posts: 78

Kudos [?]: 44 [0], given: 15

Location: United States
Concentration: Accounting, Finance
WE: Accounting (Accounting)
If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 26 Oct 2014, 17:23
4
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

82% (00:45) correct 18% (00:59) wrong based on 173 sessions

HideShow timer Statistics

If x y and z are positive is xz = 7xy ?

(1) z/y = 7
(2) x/y = 1

I am getting OA as D if I subsititute x=y, I get \(yz=7y^2=>z=7y\)
What am I missing here
[Reveal] Spoiler: OA

Last edited by Bunuel on 27 Oct 2014, 02:28, edited 1 time in total.
Renamed the topic and edited the question.

Kudos [?]: 44 [0], given: 15

1 KUDOS received
Manager
Manager
avatar
Joined: 30 Sep 2009
Posts: 115

Kudos [?]: 34 [1], given: 183

GMAT ToolKit User
Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 26 Oct 2014, 20:49
1
This post received
KUDOS
1
This post was
BOOKMARKED
To solve such type of questions we need to simplify the final question as much as possible

we need to find if xz=7xy ?

Simplifying the equation:
xz-7xy=0
x(z-7y)=0

If the options give us answers which state ,x=0 or z=7y then we can conclude that xz=7y.
Given x =positive so we need to find z=7y.

Option A : z/y=7 or z=7y ... as x,y and z are positive we know that x cannot be zero
So A is sufficient

Option B: x/y=1, as we dont know z we cannot prove xz=7xy as z is an unknown quantity.
So B insufficient

Kudos [?]: 34 [1], given: 183

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 27 Oct 2014, 02:33
If x y and z are positive is xz = 7xy ?

(1) z/y = 7 --> z = 7y. Substitute the value of z in the question: is x(7y) = 7xy. Since LHS and RHS are the same then the answer to the question is YES. Sufficient.

(2) x/y = 1 --> x = y. Substitute the value of y in the question: is xz = 7x^2 ? --> is z = 7x ? Since we cannot answer this question neither with a definite YES nor with a definite NO, the statements is not sufficient.

Answer: A.

Hope it's clear.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 132827 [0], given: 12378

Intern
Intern
avatar
Joined: 25 Sep 2014
Posts: 7

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

If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 10 Dec 2014, 16:12
As we know that x is positive, we can divide by x. So the question becomes is z=7y?

(1): z/y=7 ---> z=7y SUFFICIENT
(2): x/y=1 ---> x=y --> even if you Substitute x for y, you are still left with "is z=7x?" --> INSUFFICIENT

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

Manager
Manager
User avatar
Joined: 21 Feb 2012
Posts: 61

Kudos [?]: 60 [0], given: 63

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 11 Dec 2014, 02:17
My approach (generally speaking)

Whenever we see common terms on LHS & RHS even if they are +ve we shouldn't be in a hurry to cancel them. Set up the equation first.

xz=7xy
x(z-7y)=0
so solution is
either x=0 or z=7y
so from statement 1 we get z=7y. so sufficient
from statement 2 we don't get anything. Insufficient.

The essence in these equations/inequalities is to know the solution set and work around/from that.
my 2 cents.
_________________

Regards
J

Do consider a Kudos if you find the post useful

Kudos [?]: 60 [0], given: 63

Manager
Manager
avatar
B
Joined: 26 Jan 2015
Posts: 94

Kudos [?]: 13 [0], given: 112

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 10 Apr 2016, 20:45
Bunuel wrote:
If x y and z are positive is xz = 7xy ?

(1) z/y = 7 --> z = 7y. Substitute the value of z in the question: is x(7y) = 7xy. Since LHS and RHS are the same then the answer to the question is YES. Sufficient.

(2) x/y = 1 --> x = y. Substitute the value of y in the question: is xz = 7x^2 ? --> is z = 7x ? Since we cannot answer this question neither with a definite YES nor with a definite NO, the statements is not sufficient.

Answer: A.

Hope it's clear.



Hi Bunuel,

If the question stem were stated as x,y,z are non negative, then would the answer be still A?
_________________

Kudos is the best way to say Thank you! Please give me a kudos if you like my post

Kudos [?]: 13 [0], given: 112

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 11 Apr 2016, 00:04
Alok322 wrote:
Bunuel wrote:
If x y and z are positive is xz = 7xy ?

(1) z/y = 7 --> z = 7y. Substitute the value of z in the question: is x(7y) = 7xy. Since LHS and RHS are the same then the answer to the question is YES. Sufficient.

(2) x/y = 1 --> x = y. Substitute the value of y in the question: is xz = 7x^2 ? --> is z = 7x ? Since we cannot answer this question neither with a definite YES nor with a definite NO, the statements is not sufficient.

Answer: A.

Hope it's clear.



Hi Bunuel,

If the question stem were stated as x,y,z are non negative, then would the answer be still A?


Yes. From (1) z/y = 7, means that neither z nor y is 0. So, we'd still have the same case.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 132827 [0], given: 12378

Moderator
avatar
D
Joined: 22 Jun 2014
Posts: 942

Kudos [?]: 464 [0], given: 113

Location: India
Concentration: General Management, Technology
GMAT 1: 540 Q45 V20
GPA: 2.49
WE: Information Technology (Computer Software)
Premium Member CAT Tests
Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 11 Apr 2016, 00:43
davidfrank wrote:
If x y and z are positive is xz = 7xy ?

(1) z/y = 7
(2) x/y = 1

I am getting OA as D if I subsititute x=y, I get \(yz=7y^2=>z=7y\)
What am I missing here


whenever you see all variables involved in an equation are positive you can reduce the variables if presented on both the side.

xz = 7xy -- divide by x
z = 7y

stmt1:

z/y = 7 i.e. z=7y

stmt:2
x/y =1 ... nothing is told about z.

Answer is A.
_________________

---------------------------------------------------------------
Target - 720-740
http://gmatclub.com/forum/information-on-new-gmat-esr-report-beta-221111.html
http://gmatclub.com/forum/list-of-one-year-full-time-mba-programs-222103.html

Kudos [?]: 464 [0], given: 113

Intern
Intern
avatar
B
Joined: 20 Jul 2014
Posts: 19

Kudos [?]: 17 [0], given: 2

Location: India
GMAT 1: 710 Q46 V41
GPA: 3.16
Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 12 Aug 2016, 08:36
Hi all,

First post here. I have been lurking for a while, never had to post because the solutions were always great!

I am a bit stumped here in this question though. I know I'm doing something silly. If someone can please shed some light on what I'm doing wrong...

I chose D because, when you arrive at x = y, I just replaced x in the original stem by y. So I get zy=7y^2 and then on cancelling I come to z=7y.

Please help!

Kudos [?]: 17 [0], given: 2

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 12 Aug 2016, 08:41
Neeraj91 wrote:
Hi all,

First post here. I have been lurking for a while, never had to post because the solutions were always great!

I am a bit stumped here in this question though. I know I'm doing something silly. If someone can please shed some light on what I'm doing wrong...

I chose D because, when you arrive at x = y, I just replaced x in the original stem by y. So I get zy=7y^2 and then on cancelling I come to z=7y.

Please help!


Please check here: if-x-y-and-z-are-positive-is-xz-7xy-187488.html#p1433632 When you substitute x with y in the question, the question becomes "is z = 7x ?" Since we cannot answer this question neither with a definite YES nor with a definite NO, the statements is not sufficient.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 132827 [0], given: 12378

Intern
Intern
avatar
B
Joined: 25 Dec 2015
Posts: 4

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

Location: South Africa
Schools: HBS '20, Stanford '20
GMAT 1: 740 Q49 V42
GPA: 4
If x,y, and z are positive, is xz=7xy? [#permalink]

Show Tags

New post 21 Jul 2017, 11:15
If x, y, and z are positive, is \(xz=7xy\)?

1) \(\frac{z}{y}=7\)
2) \(\frac{x}{y}=1\)

Last edited by crosenvold on 21 Jul 2017, 11:19, edited 1 time in total.

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

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 21 Jul 2017, 11:18

Kudos [?]: 132827 [0], given: 12378

Director
Director
avatar
S
Joined: 21 Mar 2016
Posts: 536

Kudos [?]: 5 [0], given: 97

Reviews Badge CAT Tests
Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 22 Jul 2017, 03:20
davidfrank wrote:
If x y and z are positive is xz = 7xy ?

(1) z/y = 7
(2) x/y = 1

I am getting OA as D if I subsititute x=y, I get \(yz=7y^2=>z=7y\)
What am I missing here


given xz = 7xy
divide the equation by x,, gives z = 7y

stat 1: z= 7y...suff

stat 2 : x = y..not suff

ans A

Kudos [?]: 5 [0], given: 97

Expert Post
Top Contributor
SVP
SVP
User avatar
G
Joined: 12 Sep 2015
Posts: 1847

Kudos [?]: 2609 [0], given: 362

Location: Canada
Re: If x y and z are positive is xz = 7xy ? [#permalink]

Show Tags

New post 28 Sep 2017, 13:24
Expert's post
Top Contributor
davidfrank wrote:
If x y and z are positive is xz = 7xy ?

(1) z/y = 7
(2) x/y = 1


Target question: Is xz = 7xy ?
This is a good candidate for rephrasing the target question.

Since we're told that x is positive, we can take the equation xz = 7xy and divide both sides by x to get an EQUIVALENT equation: z = 7y
This allows us to REPHRASE the target question and ask an easier question....
REPHRASED target question: Is z = 7y ?

Statement 1: z/y = 7
Multiply both sides by y to get: z = 7y
Perfect - the answer to our REPHRASED target question is "Yes, z DOES equal 7y"
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: x/y = 1
Keep in mind that our REPHRASED target question asks "Is z = 7y ?"
Since statement 2 provides no information about z, we cannot determine whether or not z = 7y
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Answer:
[Reveal] Spoiler:
A


RELATED VIDEO

_________________

Brent Hanneson – Founder of gmatprepnow.com

Image

Kudos [?]: 2609 [0], given: 362

Re: If x y and z are positive is xz = 7xy ?   [#permalink] 28 Sep 2017, 13:24
Display posts from previous: Sort by

If x y and z are positive is xz = 7xy ?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.