GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 13 Dec 2019, 19:16

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

If # represents one of the operations +,- and *, is a #

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

Hide Tags

Find Similar Topics 
Manager
Manager
avatar
Joined: 16 Feb 2010
Posts: 158
If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post Updated on: 19 Sep 2010, 16:09
13
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

70% (01:33) correct 30% (02:01) wrong based on 494 sessions

HideShow timer Statistics

If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction

Originally posted by zisis on 19 Sep 2010, 15:49.
Last edited by zisis on 19 Sep 2010, 16:09, edited 1 time in total.
Manager
Manager
avatar
Joined: 23 Sep 2009
Posts: 94
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 19 Sep 2010, 16:50
1
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction



Mods, please to DS section...posted by mistake in PS - apologies


1. From choice 1 it is clear that # is subtraction. coz a+1=1+1, a*1=1*a but a-1!=(not equal) 1-a.
2. Choice 2 says directly that it is subtraction.

Hence answer is D
Manager
Manager
avatar
Joined: 04 Aug 2010
Posts: 71
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 20 Sep 2010, 19:10
1
(1) a#1 is not equal to 1#a for some numbers a

a + 1 = 1 + a for all a
a*1 = 1*a for all a

a - 1 != 1 - a

Statement (1) implies # is a minus sign, so it has same meaning as (2).

Ans D
IIMA, IIMC School Moderator
User avatar
V
Joined: 04 Sep 2016
Posts: 1370
Location: India
WE: Engineering (Other)
CAT Tests
If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 09 Sep 2019, 04:14
1
Bunuel GMATPrepNow VeritasKarishma EMPOWERgmatRichC

If a = zero, LHS = RHS , and ans to main Q stem is YES
If a\(\neq{0}\) zero, LHS\(\neq{0}\) RHS, ans to main q stem is NO.
How is St 1 suff?
_________________
It's the journey that brings us happiness not the destination.

Feeling stressed, you are not alone!!
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 59721
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 09 Sep 2019, 04:21
1
adkikani wrote:
Bunuel GMATPrepNow VeritasKarishma EMPOWERgmatRichC

If a = zero, LHS = RHS , and ans to main Q stem is YES
If a\(\neq{0}\) zero, LHS\(\neq{0}\) RHS, ans to main q stem is NO.
How is St 1 suff?


Answered here: https://gmatclub.com/forum/if-represent ... l#p1909860

From (1) we get that the equation is NOT true for ALL numbers. It's true only if a = 0 (so not for ALL numbers).
_________________
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15728
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 09 Sep 2019, 17:14
1
adkikani wrote:
Bunuel GMATPrepNow VeritasKarishma EMPOWERgmatRichC

If a = zero, LHS = RHS , and ans to main Q stem is YES
If a\(\neq{0}\) zero, LHS\(\neq{0}\) RHS, ans to main q stem is NO.
How is St 1 suff?


Hi adkikani,

This question actually has a built-in 'design flaw' which makes the information in the two Facts irrelevant. The way that the question is phrased, there are only 3 possibilities and they ALL lead to a "Sufficient" answer. There are a lot of details in the wording that make the prompt 'complicated looking' - so instead, here's a much simpler question that is based on the same design flaw:

"Is this lightbulb always on?"

IF... the lightbulb is ALWAYS on... then we have a definitive/Sufficient answer to the question that is asked (Sufficient YES).
IF... the lightbulb is NEVER on... then we also have a definitive/Sufficient answer to the question that is asked (Sufficient NO).
IF... the lightbulb is SOMETIMES on... then we still have a definitive/Sufficient answer to the question that is asked (Sufficient NO).

From the date on this post, we can clearly see that this is an old question (and it's likely that whoever wrote it didn't even recognize the flaw in it). While you'll likely see at least one Symbolism question on Test Day - and you'll certainly have to work through lots of little Arithmetic steps during the Exam - it's incredibly unlikely that you will face any flawed questions on the Official GMAT. This is all meant to say that you should ignore this question.

GMAT assassins aren't born, they're made,
Rich
_________________
Contact Rich at: Rich.C@empowergmat.com
Image


The Course Used By GMAT Club Moderators To Earn 750+

souvik101990 Score: 760 Q50 V42 ★★★★★
ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★
Manager
Manager
avatar
Joined: 20 Jul 2010
Posts: 174
GMAT ToolKit User Reviews Badge
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 19 Sep 2010, 15:58
I converted question to 3 euqations where # can be +, - or *

So
I) When # = *
ab-ac = ab-ac (true for all values)

II) When # = +
Is a+b-c=b-c

III) When #=-
Is a-b+c = -b-c?

With option A we know # is not * as 1*a is always equal to a*1. So given equation is not equal
With option B , equation is not equal.

So answer choice D
Intern
Intern
User avatar
Joined: 27 Jul 2010
Posts: 12
Location: Bangalore
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 19 Sep 2010, 19:38
vigneshpandi wrote:
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction



Mods, please to DS section...posted by mistake in PS - apologies


1. From choice 1 it is clear that # is subtraction. coz a+1=1+1, a*1=1*a but a-1!=(not equal) 1-a.
2. Choice 2 says directly that it is subtraction.

Hence answer is D



IMO, it cannot be "not equal" always.

If # is subtraction,

a#(b-c)=a-(b-c)=a-b+c

(a#b)-(a#c)=(a-b)-(a-c)=a-b-a+c=-b+c

a-b+c=-b+c when a=0 and not equal for other values.. So both are insufficient.. Am I missing something here?
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 59721
If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 20 Sep 2010, 00:14
BalakumaranP wrote:
IMO, it cannot be "not equal" always.

If # is subtraction,

a#(b-c)=a-(b-c)=a-b+c

(a#b)-(a#c)=(a-b)-(a-c)=a-b-a+c=-b+c

a-b+c=-b+c when a=0 and not equal for other values.. So both are insufficient.. Am I missing something here?


If # represents one of the operations +, - and *, is \(a#(b-c)=(a#b)-(a#c)\) for all numbers \(a\), \(b\) and \(c\).

(1) \(a#1\) is not equal to \(1#a\) for some numbers \(a\).

\(#\) is neither addition (as \(a+1=1+a\)) not multiplication (as \(a*1=1*a\)), so \(#\) is a subtraction. Then \(LHS=a#(b-c)=a-b+c\) and \(RHS=(a#b)-(a#c)=(a-b)-(a-c)=c-b\), so the question becomes "is \(a-b+c=c-b\) for all numbers \(a\), \(b\) and \(c\)?" --> "is \(a=0\)". So when \(a=0\) (and \(#\) is a subtraction) then \(a#(b-c)=(a#b)-(a#c)\) holds true but not for other values of \(a\), so not for all numbers \(a\), \(b\) and \(c\). Answer to the question is NO. Sufficient.

(2) \(#\) represents subtraction --> the same as above. Sufficient.

Answer: D.

Hope it's clear.
_________________
Intern
Intern
User avatar
Joined: 27 Jul 2010
Posts: 12
Location: Bangalore
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 20 Sep 2010, 03:09
Okay.. I read the question wrong...
Manager
Manager
avatar
Joined: 06 Aug 2010
Posts: 148
Location: Boston
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 21 Sep 2010, 10:55
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction



Mods, please to DS section...posted by mistake in PS - apologies


You're told that "#" is either addition, subtraction, or multiplication, and then asked if "#" satisfies the distributive property. Of these three, distribution only holds for multiplication, so if "#" is "*", it holds, and if "#" isn't "*", then it does not hold.

All we really need to know is what operation "#" really is.

(1) This is only true of subtraction, so # is subtraction and the distributive property does not hold. Sufficient.
(2) Same as above. Sufficient.

(D)
Retired Moderator
avatar
Joined: 29 Apr 2015
Posts: 816
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
GMAT ToolKit User
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 03 Jun 2015, 08:54
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction


Could someone edit this question so it will be an actual question? There is no proper question stem.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 59721
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 03 Jun 2015, 08:58
reto wrote:
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction


Could someone edit this question so it will be an actual question? There is no proper question stem.


What do you mean? Everything is correct there. Similar questions: Operations/functions defining algebraic/arithmetic expressions

Check functions related questions in our Special Questions Directory.

Symbols Representing Arithmetic Operation
Rounding Functions
Various Functions
_________________
Retired Moderator
avatar
Joined: 29 Apr 2015
Posts: 816
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
GMAT ToolKit User
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 03 Jun 2015, 09:07
Bunuel wrote:
reto wrote:
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction


Could someone edit this question so it will be an actual question? There is no proper question stem.


What do you mean? Everything is correct there. Similar questions: Operations/functions defining algebraic/arithmetic expressions

Check functions related questions in our Special Questions Directory.

Symbols Representing Arithmetic Operation
Rounding Functions
Various Functions



The question mark is missing in the question stem.
Senior Manager
Senior Manager
User avatar
G
Status: love the club...
Joined: 24 Mar 2015
Posts: 265
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 17 Aug 2017, 19:22
Bunuel wrote:
BalakumaranP wrote:
IMO, it cannot be "not equal" always.

If # is subtraction,

a#(b-c)=a-(b-c)=a-b+c

(a#b)-(a#c)=(a-b)-(a-c)=a-b-a+c=-b+c

a-b+c=-b+c when a=0 and not equal for other values.. So both are insufficient.. Am I missing something here?


If # represents one of the operations +, - and *, is \(a#(b-c)=(a#b)-(a#c)\) for all numbers \(a\), \(b\) and \(c\).

(1) \(a#1\) is not equal to \(1#a\) for some numbers \(a\).

\(#\) is neither addition (as \(a+1=1+a\)) not multiplication (as \(a*1=1*a\)), so \(#\) is a subtraction. Then \(LHS=a#(b-c)=a-b+c\) and \(RHS=(a#b)-(a#c)=(a-b)-(a-c)=c-b\), so the question becomes "is \(a-b+c=c-b\) for all numbers \(a\), \(b\) and \(c\)?" --> "is \(a=0\)". So when \(a=0\) (and \(#\) is a subtraction) then \(a#(b-c)=(a#b)-(a#c)\) holds true but not for other values of \(a\), so not for all numbers \(a\), \(b\) and \(c\). Answer to the question is NO. Sufficient.

(2) \(#\) represents subtraction --> the same as above. Sufficient.

Answer: D.

Hope it's clear.


I don't understand why the answer is not E. if a = 0, then yes, if a is not equal to 0, then no. So not sufficient, as nothing can be said conclusively ...
anybody out there to help me ....?

thanks
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 59721
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 17 Aug 2017, 21:24
gmatcracker2017 wrote:
Bunuel wrote:
BalakumaranP wrote:
IMO, it cannot be "not equal" always.

If # is subtraction,

a#(b-c)=a-(b-c)=a-b+c

(a#b)-(a#c)=(a-b)-(a-c)=a-b-a+c=-b+c

a-b+c=-b+c when a=0 and not equal for other values.. So both are insufficient.. Am I missing something here?


If # represents one of the operations +, - and *, is \(a#(b-c)=(a#b)-(a#c)\) for all numbers \(a\), \(b\) and \(c\).

(1) \(a#1\) is not equal to \(1#a\) for some numbers \(a\).

\(#\) is neither addition (as \(a+1=1+a\)) not multiplication (as \(a*1=1*a\)), so \(#\) is a subtraction. Then \(LHS=a#(b-c)=a-b+c\) and \(RHS=(a#b)-(a#c)=(a-b)-(a-c)=c-b\), so the question becomes "is \(a-b+c=c-b\) for all numbers \(a\), \(b\) and \(c\)?" --> "is \(a=0\)". So when \(a=0\) (and \(#\) is a subtraction) then \(a#(b-c)=(a#b)-(a#c)\) holds true but not for other values of \(a\), so not for all numbers \(a\), \(b\) and \(c\). Answer to the question is NO. Sufficient.

(2) \(#\) represents subtraction --> the same as above. Sufficient.

Answer: D.

Hope it's clear.


I don't understand why the answer is not E. if a = 0, then yes, if a is not equal to 0, then no. So not sufficient, as nothing can be said conclusively ...
anybody out there to help me ....?

thanks


The question asks: is \(a#(b-c)=(a#b)-(a#c)\) for all numbers \(a\), \(b\) and \(c\)? From each statement we got a deinite NO answer - NO the equation doe NOT hold true for all numbers, it's true if a = 0 but not true if a is not 0.
_________________
Senior Manager
Senior Manager
User avatar
G
Status: love the club...
Joined: 24 Mar 2015
Posts: 265
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 17 Aug 2017, 22:01
gmatcracker2017 wrote:
Bunuel wrote:
BalakumaranP wrote:
IMO, it cannot be "not equal" always.

If # is subtraction,

a#(b-c)=a-(b-c)=a-b+c

(a#b)-(a#c)=(a-b)-(a-c)=a-b-a+c=-b+c

a-b+c=-b+c when a=0 and not equal for other values.. So both are insufficient.. Am I missing something here?


If # represents one of the operations +, - and *, is \(a#(b-c)=(a#b)-(a#c)\) for all numbers \(a\), \(b\) and \(c\).

(1) \(a#1\) is not equal to \(1#a\) for some numbers \(a\).

\(#\) is neither addition (as \(a+1=1+a\)) not multiplication (as \(a*1=1*a\)), so \(#\) is a subtraction. Then \(LHS=a#(b-c)=a-b+c\) and \(RHS=(a#b)-(a#c)=(a-b)-(a-c)=c-b\), so the question becomes "is \(a-b+c=c-b\) for all numbers \(a\), \(b\) and \(c\)?" --> "is \(a=0\)". So when \(a=0\) (and \(#\) is a subtraction) then \(a#(b-c)=(a#b)-(a#c)\) holds true but not for other values of \(a\), so not for all numbers \(a\), \(b\) and \(c\). Answer to the question is NO. Sufficient.

(2) \(#\) represents subtraction --> the same as above. Sufficient.

Answer: D.

Hope it's clear.


I don't understand why the answer is not E. if a = 0, then yes, if a is not equal to 0, then no. So not sufficient, as nothing can be said conclusively ...
anybody out there to help me ....?

thanks


Thanks Bunuel, you are soooo... great .... :clap:
Senior Manager
Senior Manager
avatar
S
Joined: 15 Jan 2017
Posts: 332
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 14 Sep 2017, 15:09
Key word in A --> 'not equal to' -- thus the only time a#1 not 1#a is when # = minus
Really need to read questions properly!
Senior Manager
Senior Manager
avatar
S
Joined: 15 Jan 2017
Posts: 332
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 14 Sep 2017, 15:10
Key word in A --> 'not equal to' -- thus the only time a#1 not 1#a is when # = minus
Really need to read questions properly!
SVP
SVP
User avatar
D
Joined: 03 Jun 2019
Posts: 1885
Location: India
Premium Member Reviews Badge CAT Tests
Re: If # represents one of the operations +,- and *, is a #  [#permalink]

Show Tags

New post 09 Sep 2019, 04:53
zisis wrote:
If # represents one of the operations +,- and *, is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a

(2) # represents subtraction


Given: # represents one of the operations +,- and *

Asked: Is a # (b-c) = (a#b) – (a#c) for all numbers a, b and c.

(1) a#1 is not equal to 1#a for some numbers a
a+1 = 1+a
a*1 = 1*a
\(a-1 \neq 1-a\)
# = -
a#(b-c) = a-b+c
(a#b) – (a#c) = (a-b) - (a-c) = c -b
a # (b-c)\(\neq\) (a#b) – (a#c)
SUFFICIENT

(2) # represents subtraction
# = -
a#(b-c) = a-b+c
(a#b) – (a#c) = (a-b) - (a-c) = c -b
a # (b-c)\(\neq\) (a#b) – (a#c)
SUFFICIENT

IMO D
GMAT Club Bot
Re: If # represents one of the operations +,- and *, is a #   [#permalink] 09 Sep 2019, 04:53
Display posts from previous: Sort by

If # represents one of the operations +,- and *, is a #

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





cron

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