Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 06 May 2015, 05:30

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# 1/ If the operation # is defined for all integers a and b by

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
SVP
Joined: 05 Jul 2006
Posts: 1519
Followers: 5

Kudos [?]: 115 [0], given: 39

1/ If the operation # is defined for all integers a and b by [#permalink]  15 Oct 2006, 08:41
1/ If the operation # is defined for all integers a and b by
a#b = a + b - ab which of the followin statements must be true for all integers a,b, and c?

A) a#b= b#a
B) a#0= a
C) (a#b)#C = a#(b#c)

it is abvious that A,B are true lets check three

a#b = a+b-ab , b#c = b+c - bc

(a+b-ab)#c = a+b-ab+c - ac-bc+abc

(b+c - bc)#a = a+b+c -bc - ab-ac+abc

thus my answer is A,B ONLY
Manager
Joined: 02 Oct 2006
Posts: 54
Location: Paris
Followers: 0

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

[#permalink]  15 Oct 2006, 09:12
First, thanks for seperating the posts...
sorry, next time will be careful!!

In fact for this question, the answer is A,B a,d C!!!
The question was on GMATprep so I only have the answer and not the explanations...

Zz
SVP
Joined: 05 Jul 2006
Posts: 1519
Followers: 5

Kudos [?]: 115 [0], given: 39

[#permalink]  15 Oct 2006, 09:35
so wut is the answer
Manager
Joined: 27 Mar 2008
Posts: 53
Followers: 1

Kudos [?]: 6 [0], given: 0

Re: Zamzim separate posts [#permalink]  29 Mar 2008, 18:25
a#b = a + b - ab

We already know that (A) and (B) are true.

C) (a#b)#C = a#(b#c)

LS
= (a+b-ab) + c - (a+b-ab)*c
= a + b - ab + c - ac - bc + abc
= a + b + c - ab - ac - bc + abc (reordering)

RS
= a + (b+c-bc) - a(b+c-bc)
= a + b + c - bc -ab -ac + abc
= a + b + c - ab - ac - bc + abc

Therefore, LS=RS and all of A, B, and C are true.

I think it's the confusion caused when multiplying all the terms. We just gotta be extra careful, which is tough when we're rushed to do these questions in 2 minutes!
Re: Zamzim separate posts   [#permalink] 29 Mar 2008, 18:25
Similar topics Replies Last post
Similar
Topics:
24 If the operation @ is defined for all integers a and b 17 18 Sep 2010, 19:16
If the operation * is defined for all integers a and b by 2 31 Jan 2008, 18:36
If the operation * is defined for all integers a and b by 5 06 Jan 2008, 15:34
If the operation (*) is defined for all integers a and b by 6 01 Oct 2007, 15:04
if the operation & is defined for all integers a and b 6 08 Nov 2005, 21:22
Display posts from previous: Sort by

# 1/ If the operation # is defined for all integers a and b by

 Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO 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®.