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

It is currently 23 Apr 2019, 17:08

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

Is ab = 9c^2–4?

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

Hide Tags

 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 54493
Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 12 Feb 2015, 07:07
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

78% (01:36) correct 22% (01:47) wrong based on 150 sessions

HideShow timer Statistics

Manager
Manager
User avatar
Joined: 03 Oct 2014
Posts: 127
Location: India
Concentration: Operations, Technology
GMAT 1: 720 Q48 V40
WE: Engineering (Aerospace and Defense)
Reviews Badge
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 12 Feb 2015, 07:58
C - Using A & B....A= 3c+2, B= 3c-2
Manager
Manager
avatar
Joined: 14 Jul 2014
Posts: 91
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 13 Feb 2015, 00:22
1
Ans C

Stmnt 1 -Nothing about b - Not Suff
Stmnt 2 - Nothing about a - Not Suff

Combining, a = 3c + 6 and b = 3c - 2
Possible to compute and answer the Question - Hence Suff !

Ans - C
Intern
Intern
avatar
Joined: 22 Aug 2014
Posts: 40
GMAT ToolKit User
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 13 Feb 2015, 01:29
1
Bunuel wrote:
Is ab = 9c^2–4?

(1) a divided by 3 is equal to c with a remainder of 2.
(2) b divided by 3 is equal to c minus 2/3.

Kudos for a correct solution.


1. a = 3c+6
2. b = 3c-2

therefore ab = (3c+6)*(3c-2) = 9C^2+12C-12 <> 9C^2 - 4

Option C
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 54493
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 16 Feb 2015, 06:18
Bunuel wrote:
Is ab = 9c^2–4?

(1) a divided by 3 is equal to c with a remainder of 2.
(2) b divided by 3 is equal to c minus 2/3.

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION

Solution: C

Statement (1) says nothing about b; INSUFFICIENT. Statement (2) says nothing about a; INSUFFICIENT. When combining the statements, be sure to simplify them first. If a/3 = c with a remainder of 2, then a = 3c + 2. If b/3 = c – 2/3, then b = 3c-2. Thus ab = (3c+2)(3c-2), or 9c^2–4; (C).
_________________
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13969
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 19 Feb 2015, 20:16
Hi buddyisraelgmat and aj13783,

While you both selected the correct answer, you both made the same "math mistake" in your work. While that error didn't hurt you on this question, it might impact other questions in the future, so it's worth 'fixing.'

In Fact 1, we're told that when A is divided by 3 equals C with a remainder of 2. This translates into:

A/3 = C remainder 2

If you want to isolate the A, then you multiply both sides by 3, BUT you do NOT multiply the remainder (since the remainder represents the "leftover pieces" and that part does NOT get tripled).

So

A = 3C + 2 (not A = 3C + 6)

Here is an example of that, using real numbers.....

Let's say A = 14

14/3 = 4 remainder 2

14 = 3(4) + 2

GMAT assassins aren't born, they're made,
Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****

Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save $75 + GMAT Club Tests Free
  Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/
Intern
Intern
avatar
Joined: 29 Jun 2016
Posts: 1
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 18 Jul 2016, 12:37
Bunuel wrote:
Bunuel wrote:
Is ab = 9c^2–4?

(1) a divided by 3 is equal to c with a remainder of 2.
(2) b divided by 3 is equal to c minus 2/3.

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION

Solution: C

Statement (1) says nothing about b; INSUFFICIENT. Statement (2) says nothing about a; INSUFFICIENT. When combining the statements, be sure to simplify them first. If a/3 = c with a remainder of 2, then a = 3c + 2. If b/3 = c – 2/3, then b = 3c-2. Thus ab = (3c+2)(3c-2), or 9c^2–4; (C).


Hi,
I understand that a = 3c+2 but how is B = 3c-2? B leaves a remainder of -2/3. Please double check.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 54493
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 18 Jul 2016, 23:56
1
ajxxatic wrote:
Bunuel wrote:
Bunuel wrote:
Is ab = 9c^2–4?

(1) a divided by 3 is equal to c with a remainder of 2.
(2) b divided by 3 is equal to c minus 2/3.

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION

Solution: C

Statement (1) says nothing about b; INSUFFICIENT. Statement (2) says nothing about a; INSUFFICIENT. When combining the statements, be sure to simplify them first. If a/3 = c with a remainder of 2, then a = 3c + 2. If b/3 = c – 2/3, then b = 3c-2. Thus ab = (3c+2)(3c-2), or 9c^2–4; (C).


Hi,
I understand that a = 3c+2 but how is B = 3c-2? B leaves a remainder of -2/3. Please double check.


(2) b divided by 3 is equal to c minus 2/3.

b/3 = c - 2/3;

Multiply by 3: b = 3c - 2.

Hope it's clear.
_________________
Director
Director
avatar
S
Joined: 12 Nov 2016
Posts: 725
Location: United States
Schools: Yale '18
GMAT 1: 650 Q43 V37
GRE 1: Q157 V158
GPA: 2.66
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 17 Jul 2017, 18:06
Bunuel wrote:
Is ab = 9c^2–4?

(1) a divided by 3 is equal to c with a remainder of 2.
(2) b divided by 3 is equal to c minus 2/3.

Kudos for a correct solution.


Before looking at the statements we can easily see that this question is just a variation of (a+b)(a-b) - a common theme on the GMAT- (3b-2)(3b +2)

Statement 1

If a/3 = c remainder 2 then = a= 3c +2

but no info about "b" insuff

Statement 2

Same thing

b/3= c-2/3 - use algebra
b= 3c- 2

no info about

a

St 1 & 2

(3c-2)(3c +2) suff

c
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 10619
Re: Is ab = 9c^2–4?  [#permalink]

Show Tags

New post 19 Mar 2019, 09:37
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 Club Bot
Re: Is ab = 9c^2–4?   [#permalink] 19 Mar 2019, 09:37
Display posts from previous: Sort by

Is ab = 9c^2–4?

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


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| 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®.