If the operation * is defined for all integers a and b by : Quant Question Archive [LOCKED]
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 24 Jan 2017, 10:46

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

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

If the operation * is defined for all integers a and b by

Author Message
Manager
Joined: 23 Jan 2008
Posts: 108
Followers: 2

Kudos [?]: 75 [0], given: 0

If the operation * is defined for all integers a and b by [#permalink]

Show Tags

31 Jan 2008, 18:36
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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 ?

1. a*b = b*a
2. a*0 = a
3. (a*b)*c = a*(b*c)

- 1 only
- 2 only
- 1 and 2 only
- 1 and 3 only
- 1,2 and 3
CEO
Joined: 29 Mar 2007
Posts: 2583
Followers: 19

Kudos [?]: 422 [0], given: 0

Show Tags

31 Jan 2008, 18:48
blog wrote:
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 ?

1. a*b = b*a
2. a*0 = a
3. (a*b)*c = a*(b*c)

- 1 only
- 2 only
- 1 and 2 only
- 1 and 3 only
- 1,2 and 3

This problem is listed here somewherez.

I: a+b-ab= b+a-ba OK
II: a+0-(a)0=0+a-0(a) OK same thing

III: is def intimidating. just work it like the functions in the MGMAT book if you have that:

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

a+b+c-ab-ac-bc-abc=a+b+c-ab-ac-bc-abc Everything cancels out! So suff.

E
SVP
Joined: 28 Dec 2005
Posts: 1575
Followers: 3

Kudos [?]: 148 [0], given: 2

Show Tags

31 Jan 2008, 20:29
agree with E. The only tough one to work one is option 3, but expand it and youll see theyre the same
Re: operation   [#permalink] 31 Jan 2008, 20:29
Display posts from previous: Sort by