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
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
Live EA class + 6 months of EA OnDemand
  • Expert-led weekly online sessions
  • EA Masterclass access between classes
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.

130-point 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.

GMATPrep Algebra

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 170
Joined: Mon Oct 22, 2007 4:36 am
Thanked: 7 times
by erjamit » Thu Aug 07, 2008 5:58 am
Hi,
Pls help with this.

If the operation (*) is defined for all integers a and b by a (*) b = a + b - ab, which of the following statements must be true for all integers, a, b, and c?

I. a (*) b = b (*) a
II. a (*) 0 = a
III. (a*b)*c = a*(b*c)

A) I
B) II
C) I,II
D) I,III
E) I,II,III

I couldn't figure out why III is true. Can someon explain how to derive III.

OA E

Thanks
Amit
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Senior | Next Rank: 100 Posts
Posts: 58
Joined: Fri Jul 18, 2008 12:26 pm
Thanked: 2 times

by malolakrupa » Thu Aug 07, 2008 10:23 am
I think the answer is C .
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 170
Joined: Mon Oct 22, 2007 4:36 am
Thanked: 7 times

by erjamit » Thu Aug 07, 2008 10:25 am
As already told OA is E.

Pls explain why the III option is correct.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1153
Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members
Thanked: 146 times

by parallel_chase » Thu Aug 07, 2008 10:48 am
III. (a*b)*c = a*(b*c)


Let (a*b) = y = a+b-2ab

y*c = y + c -2yc = a+b-ab +c - 2c(a+b-2ab) = a+b+c-2ab-2ac-2bc+4abc

Let (b*c) = x = b+c-2bc

a*x = a+x-2ax = a+b+c-2bc-2a(b+c-2bc) = a+b+c-2ab-2ac-2bc+4abc


Hence the answer is E.

Hope this helps.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 170
Joined: Mon Oct 22, 2007 4:36 am
Thanked: 7 times

by erjamit » Thu Aug 07, 2008 10:53 am
(a*b)*c = (a + b - ab)*c
= a + b - ab + c - (a + b - ab)c


a*(b*c) = a*(b+c-bc)
= a + b +c - bc - a(b+c-bc)

What is wrong with my approach?

Thanks
Amit
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1153
Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members
Thanked: 146 times

by parallel_chase » Thu Aug 07, 2008 11:04 am
erjamit wrote:(a*b)*c = (a + b - ab)*c
= a + b - ab + c - (a + b - ab)c
absolutely nothing is wrong with your approach, If you expand,

a+b-ab+c-ac-bc+abc -------I
a*(b*c) = a*(b+c-bc)
= a + b +c - bc - a(b+c-bc)
a+b+c -bc-ab-ac+abc -------II

If you compare I and II both are equal.

In fact i took the a*b = a+b-2ab instead of a+b-ab

But it doesnt matter as you can see one can still get E as the answer.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 170
Joined: Mon Oct 22, 2007 4:36 am
Thanked: 7 times

by erjamit » Thu Aug 07, 2008 11:06 am
This is what nerves do to you. :( ......

I just solved till this part and then glanced at both options and eliminated it.

Thanks mate.

Amit
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1169
Joined: Sun Jul 06, 2008 2:34 amFollowed by: 1 member
Thanked: 25 times

by aj5105 » Thu Oct 02, 2008 5:53 am
imo, one of better ways to solve these kind of problems is use numbers.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: Sun Aug 10, 2008 6:04 pm

Very Confused

by olpre4 » Mon Nov 24, 2008 7:56 pm
1) What is being tested in this problem?

2) Operationally, how did you get

From (a*b)*c = (a + b - ab)*c

To = a + b - ab + c - (a + b - ab)c
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 708
Joined: Sun Jun 01, 2008 4:59 amFollowed by: 1 member
Location: USA
Thanked: 13 times

by niraj_a » Tue Nov 25, 2008 5:10 pm
you could try picking numbers abd testing this out too....
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1