BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

★★★★★5.0559 reviews
Vote for Target Test Prep, Newsweek Readers’ Choice Awards 2026
NEWSWEEK READERS’ CHOICE 2026

BIG NEWS! Target Test Prep has been nominated, and they’d love your vote!

TTP has worked incredibly hard to build the best test prep experience possible, and winning Newsweek’s 2026 Readers’ Choice Award for Best Test Prep would mean a lot to them. If TTP has helped you, they’d be incredibly grateful for your vote. You can vote once each day through September 9.

Vote for TTP
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

Manhattan gmat DS question - doesn't make sense

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 4
Joined: Wed Feb 25, 2009 7:31 am
by sk123 » Wed Feb 25, 2009 10:12 am
Does anyone get this manhattan gmat question. I tried to understand their reason but it didn't make any sense ... just wanna see if anyone has another way of doing it.

If a^2 is not equal to b^2, what is the value of

a - b
__________ ?
a^2 – b^2



(1) 3^b + 2 = 81

(2) a = 3^2b – 3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 68
Joined: Sun Dec 21, 2008 12:00 am
Thanked: 3 times

by ontopofit » Wed Feb 25, 2009 11:36 am
IMO C
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 4
Joined: Wed Feb 25, 2009 7:31 am

by sk123 » Wed Feb 25, 2009 11:52 am
Here's the answer:

(1) SUFFICIENT: We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2.

We can plug this value into the equation a = 3b – 1 to solve for a.

(2) SUFFICIENT: We can set the right side of this equation equal to the right side of the equation in the question (both sides equal a). 3b – 1 = 32b – 3, which means that b – 1 = 2b – 3 and therefore b = 2.

We can plug this value into the equation a = 3b – 1 to solve for a.

The correct answer is D.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 377
Joined: Wed Sep 03, 2008 9:30 amFollowed by: 2 members
Thanked: 15 times

by schumi_gmat » Wed Feb 25, 2009 12:14 pm
we have to find 1/(a+b). The a-b can be cancelled as a-b not equal to 0

From A) 3^(b+2) = 81, i.e. b+2=4 and b=2

We dont know value of a. Hence insuff

From B) a= 3^2b-3

one equation, 2 variables. Hence insuff

Hence ans is C.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 4
Joined: Wed Feb 25, 2009 7:31 am

by sk123 » Wed Feb 25, 2009 3:48 pm
The answer I posted above is from Manhattan gmat ... from one of the online exams ...
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 42
Joined: Thu Feb 19, 2009 10:26 am
Thanked: 3 times
GMAT Score:720

by mygmat.2009 » Wed Feb 25, 2009 6:41 pm
I agree with schumi_gmat , unless sky123 is missing to give us part of the question!

Sky123, in your answer you mention equation [a = 3b – 1], yet the question you posted does not mention this equality.


Sam
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 986
Joined: Wed Dec 20, 2006 11:07 amFollowed by: 1 member
Location: India
Thanked: 51 times

by gabriel » Thu Feb 26, 2009 9:49 am
sk123 wrote:Here's the answer:

(1) SUFFICIENT: We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2.

We can plug this value into the equation a = 3b – 1 to solve for a.

(2) SUFFICIENT: We can set the right side of this equation equal to the right side of the equation in the question (both sides equal a). 3b – 1 = 32b – 3, which means that b – 1 = 2b – 3 and therefore b = 2.

We can plug this value into the equation a = 3b – 1 to solve for a.

The correct answer is D.
Where did you get a=3b-1 from?, it is not part of the question. So if the question is correct then schumi_gmat is correct.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 4
Joined: Wed Feb 25, 2009 7:31 am

by sk123 » Thu Feb 26, 2009 1:44 pm
That's what I was trying to get at ... that is the official answer from the manhattan gmat exam. I was thinking I might be missing something but I guess their expl doesn't add up.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Master | Next Rank: 500 Posts
Posts: 229
Joined: Tue Jan 13, 2009 6:56 am
Thanked: 8 times
GMAT Score:700

by Uri » Thu Feb 26, 2009 2:17 pm
utterly confused! first i thought MGMAT has used technique to convert decimal number to a different base (base of 3 in stead of base of 10). but after following more carefully i understood that it was not so. don't understand from where they have got the other equation.

sk123, if you enclosed the exponents within brackets, that would have been better for understanding. but any way, this solution by MGMAT is very confusing.

if the question and the solution is reproduced correctly, then can any MGMAT tutor available here please help us?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 15
Joined: Thu May 01, 2008 9:57 pm
Thanked: 2 times

by fleshins » Sat Feb 28, 2009 10:24 pm
how does this make any sense either?

"We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2."

Thanks for the explanation, if there is one ...
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1