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

Redeem

How to solve this

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 172
Joined: Wed Oct 31, 2007 11:21 am
Thanked: 1 times

How to solve this

by gmattester » Thu Aug 21, 2008 6:17 pm
For any numbers a and b, a ◦ b = a + b – ab.
If a ◦ b = 0. which of the following CANNOT be a value of b?
(A) 2
(B) 1
(C) 0
(D) -1
(E) 2

After getting ab=a+b, looks like all can be values of b
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 144
Joined: Thu Apr 17, 2008 3:33 pm
Thanked: 8 times

Re: How to solve this

by Sunny22uk » Thu Aug 21, 2008 6:31 pm
gmattester wrote:For any numbers a and b, a ◦ b = a + b – ab.
If a ◦ b = 0. which of the following CANNOT be a value of b?
(A) 2
(B) 1
(C) 0
(D) -1
(E) 2

After getting ab=a+b, looks like all can be values of b
if you substitute b as 1, you get a=a+1 which cannot be true.
The OA should be be B
You cannot discover new oceans unless you have the courage to loose sight of the shore.
Top
Master | Next Rank: 500 Posts
Posts: 172
Joined: Wed Oct 31, 2007 11:21 am
Thanked: 1 times

Re: How to solve this

by gmattester » Thu Aug 21, 2008 6:57 pm
Sunny22uk wrote:
gmattester wrote:For any numbers a and b, a ◦ b = a + b – ab.
If a ◦ b = 0. which of the following CANNOT be a value of b?
(A) 2
(B) 1
(C) 0
(D) -1
(E) 2

After getting ab=a+b, looks like all can be values of b
if you substitute b as 1, you get a=a+1 which cannot be true.
The OA should be be B
Got cha.....
Thanks
Top
Legendary Member
Posts: 891
Joined: Sat Aug 16, 2008 4:21 am
Thanked: 27 times
Followed by:1 members
GMAT Score:660(

Re: How to solve this

by 4meonly » Fri Aug 22, 2008 5:45 am
Sunny22uk wrote:
gmattester wrote:For any numbers a and b, a ◦ b = a + b – ab.
If a ◦ b = 0. which of the following CANNOT be a value of b?
(A) 2
(B) 1
(C) 0
(D) -1
(E) 2

After getting ab=a+b, looks like all can be values of b
if you substitute b as 1, you get a=a+1 which cannot be true.
The OA should be be B
So, what is the answer?
Top
Junior | Next Rank: 30 Posts
Posts: 29
Joined: Thu Jul 24, 2008 4:38 pm
Thanked: 1 times

by leugene » Fri Aug 22, 2008 1:49 pm
Algebraically, if you think about it this way:

a+b-ab=0

a-ab=-b (just reworking the problem to isolate a)

a(1-b)=-b (still working)

a=[(-b)/(1-b)]

And since you can't have 0 be in the denominator, the only way that would occur is if b=1. Therefore, b cannot equal 1, so answer is B.
Top
Post new topic Post Reply
• Page 1 of 1