It is currently 23 Oct 2017, 23:07

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 (a – b)2c = 0, then which of the following must be true?

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

Hide Tags

1 KUDOS received
Manager
Manager
avatar
Joined: 15 Mar 2012
Posts: 57

Kudos [?]: 22 [1], given: 19

Location: United States
Concentration: Marketing, Strategy
If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 10:18
1
This post received
KUDOS
5
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

53% (00:47) correct 47% (00:44) wrong based on 300 sessions

HideShow timer Statistics

If ((a – b)^2)c = 0, then which of the following must be true?

I. a = b
II. (a – b) c = 0
III. c = 0

A. II only
B. I and II only
C. I and III only
D. II and III only
E. I, II, and III
[Reveal] Spoiler: OA

_________________

MV
"Better to fight for something than live for nothing.” ― George S. Patton Jr


Last edited by marcovg4 on 30 Mar 2013, 10:32, edited 1 time in total.

Kudos [?]: 22 [1], given: 19

1 KUDOS received
VP
VP
User avatar
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1120

Kudos [?]: 2334 [1], given: 219

Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
GMAT ToolKit User
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 10:28
1
This post received
KUDOS
\(c(a-b)^2=0\)

In this case we have 2 options
\(c=0\) or \((a-b)^2=0, a-b=0\)

I.a = b a-b=0
This can be false, if c = 0

II. (a – b) c = 0
We know that one (or both) between \(c\) and \(a-b\) equals 0, so when you multiply a 0 by any number you obtain 0. This must be true

III.c = 0
This can be false if a-b=0
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

Kudos [?]: 2334 [1], given: 219

Manager
Manager
avatar
Joined: 15 Mar 2012
Posts: 57

Kudos [?]: 22 [0], given: 19

Location: United States
Concentration: Marketing, Strategy
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 10:34
Zarrolou,

I forgot to write the answer choice. Try again please.
_________________

MV
"Better to fight for something than live for nothing.” ― George S. Patton Jr

Kudos [?]: 22 [0], given: 19

Manager
Manager
avatar
Joined: 15 Mar 2012
Posts: 57

Kudos [?]: 22 [0], given: 19

Location: United States
Concentration: Marketing, Strategy
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 10:39
Can you explain why? I thought III option is true, since it is saying that c = 0, hence (a-b)^2 * c = 0
_________________

MV
"Better to fight for something than live for nothing.” ― George S. Patton Jr

Kudos [?]: 22 [0], given: 19

VP
VP
User avatar
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1120

Kudos [?]: 2334 [0], given: 219

Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
GMAT ToolKit User
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 10:47
marcovg4 wrote:
Can you explain why? I thought III option is true, since it is saying that c = 0, hence (a-b)^2 * c = 0


Option III says that, given \((a-b)^2 * c = 0\), c must be =0.
Try with numbers : \((5-5)^2 * 1000 = 0\); in this (a-b)^2 * c = 0 but c = 1000, not 0. So III can be false as you see.
It's the same reason why you exclude option I. We know that one term (c, or a-b) must be =0, but we don't know which one. Option I and III exclude the other term saying respectively that a-b=0 and c=0, on the other hand option II is correct because makes no assumption: c(a-b)=0 => we know that at least one of those therms is 0 (and the option doesn't specify which one, that's the point) , so 0*(a-b)=0 or c*(0)=0 => always TRUE.

Hope it's clear
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

Kudos [?]: 2334 [0], given: 219

Manager
Manager
avatar
Joined: 15 Mar 2012
Posts: 57

Kudos [?]: 22 [0], given: 19

Location: United States
Concentration: Marketing, Strategy
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 11:06
Zarrolou wrote:
marcovg4 wrote:
Can you explain why? I thought III option is true, since it is saying that c = 0, hence (a-b)^2 * c = 0


Option III says that, given \((a-b)^2 * c = 0\), c must be =0.
Try with numbers : \((5-5)^2 * 1000 = 0\); in this (a-b)^2 * c = 0 but c = 1000, not 0. So III can be false as you see.
It's the same reason why you exclude option I. We know that one term (c, or a-b) must be =0, but we don't know which one. Option I and III exclude the other term saying respectively that a-b=0 and c=0, on the other hand option II is correct because makes no assumption: c(a-b)=0 => we know that at least one of those therms is 0 (and the option doesn't specify which one, that's the point) , so 0*(a-b)=0 or c*(0)=0 => always TRUE.

Hope it's clear


I agree with you, I have to understand the "right" approach to this kind of questions :?
_________________

MV
"Better to fight for something than live for nothing.” ― George S. Patton Jr

Kudos [?]: 22 [0], given: 19

Moderator
Moderator
User avatar
G
Joined: 01 Sep 2010
Posts: 3355

Kudos [?]: 9099 [0], given: 1155

Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 30 Mar 2013, 12:26
marcovg4 wrote:
Zarrolou wrote:
marcovg4 wrote:
Can you explain why? I thought III option is true, since it is saying that c = 0, hence (a-b)^2 * c = 0


Option III says that, given \((a-b)^2 * c = 0\), c must be =0.
Try with numbers : \((5-5)^2 * 1000 = 0\); in this (a-b)^2 * c = 0 but c = 1000, not 0. So III can be false as you see.
It's the same reason why you exclude option I. We know that one term (c, or a-b) must be =0, but we don't know which one. Option I and III exclude the other term saying respectively that a-b=0 and c=0, on the other hand option II is correct because makes no assumption: c(a-b)=0 => we know that at least one of those therms is 0 (and the option doesn't specify which one, that's the point) , so 0*(a-b)=0 or c*(0)=0 => always TRUE.

Hope it's clear


I agree with you, I have to understand the "right" approach to this kind of questions :?



basically what Zarrolou says, is that in I and III you have not sufficient information to answer the question (remember is a MUST be true question, not a maybe question)

In fact rephrasing the question you have (a-b)*c=0. you have to have all the elements to say for sure that the equation is equal to zero.

Only the II one works.
_________________

COLLECTION OF QUESTIONS AND RESOURCES
Quant: 1. ALL GMATPrep questions Quant/Verbal 2. Bunuel Signature Collection - The Next Generation 3. Bunuel Signature Collection ALL-IN-ONE WITH SOLUTIONS 4. Veritas Prep Blog PDF Version 5. MGMAT Study Hall Thursdays with Ron Quant Videos
Verbal:1. Verbal question bank and directories by Carcass 2. MGMAT Study Hall Thursdays with Ron Verbal Videos 3. Critical Reasoning_Oldy but goldy question banks 4. Sentence Correction_Oldy but goldy question banks 5. Reading-comprehension_Oldy but goldy question banks

Kudos [?]: 9099 [0], given: 1155

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 16525

Kudos [?]: 274 [0], given: 0

Premium Member
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 10 Jan 2015, 19:57
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Kudos [?]: 274 [0], given: 0

Intern
Intern
User avatar
Joined: 17 Jun 2015
Posts: 12

Kudos [?]: [0], given: 58

GPA: 3.35
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 08 Jul 2015, 03:38
marcovg4 wrote:
If ((a – b)^2)c = 0, then which of the following must be true?

I. a = b
II. (a – b) c = 0
III. c = 0

A. II only
B. I and II only
C. I and III only
D. II and III only
E. I, II, and III


i'm wrong again

i thought C is the answer. but it can't be true while C=0. if it is then equation will be 0. So a=b is only solution

Kudos [?]: [0], given: 58

Expert Post
2 KUDOS received
Optimus Prep Instructor
User avatar
B
Joined: 06 Nov 2014
Posts: 1905

Kudos [?]: 526 [2], given: 23

If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 08 Jul 2015, 23:42
2
This post received
KUDOS
Expert's post
If ((a – b)^2)c = 0, then which of the following must be true?

This would be zero if a = b or if c = 0 (or both of these cases). We can't say that a must be equal to b because c could be zero. Eliminate B, C, and E. Since the remaining choices both have II evaluate III. c need not be zero since a can equal b. Eliminate D.
I. a = b
II. (a – b) c = 0
III. c = 0

A. II only
B. I and II only
C. I and III only
D. II and III only
E. I, II, and III
_________________

Janielle Williams

Customer Support

Special Offer: $80-100/hr. Online Private Tutoring
GMAT On Demand Course $299
Free Online Trial Hour

Kudos [?]: 526 [2], given: 23

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 16525

Kudos [?]: 274 [0], given: 0

Premium Member
Re: If (a – b)2c = 0, then which of the following must be true? [#permalink]

Show Tags

New post 10 Sep 2017, 10:42
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Kudos [?]: 274 [0], given: 0

Re: If (a – b)2c = 0, then which of the following must be true?   [#permalink] 10 Sep 2017, 10:42
Display posts from previous: Sort by

If (a – b)2c = 0, then which of the following must be true?

  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®.