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

It is currently 15 Sep 2014, 19:34

Close

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If AB = 40, what is the value of AB(A + 2B)? (1) A ? B =

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 07 Aug 2004
Posts: 20
Followers: 0

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

If AB = 40, what is the value of AB(A + 2B)? (1) A ? B = [#permalink] New post 19 Aug 2004, 23:49
If AB = 40, what is the value of AB(A + 2B)?

(1) A ? B = -18.

(2) A²B = 80.


(a) Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.

(b) Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.

(c) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.

(d) Either statement BY ITSELF is sufficient to answer the question.

(e) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, requiring more data pertaining to the problem.
Intern
Intern
avatar
Joined: 07 Aug 2004
Posts: 20
Followers: 0

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

 [#permalink] New post 19 Aug 2004, 23:53
If AB = 40, what is the value of AB(A + 2B)?

(1) A - B = -18.

(2) A²B = 80.


a) Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.

b ) Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.

c) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.

d) Either statement BY ITSELF is sufficient to answer the question.

e) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, requiring more data pertaining to the problem.
Director
Director
avatar
Joined: 20 Jul 2004
Posts: 593
Followers: 1

Kudos [?]: 22 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Aug 2004, 00:03
If AB = 40, what is the value of AB(A + 2B)?

(1) A - B = -18.
AB = 40
A(A+18) = 40
A^2 + 18A - 40 = 0
A = -20 or 2
B = -2 or 20
Cannot find.

(2) A²B = 80.
A²B = 80.
AB = 40
A = 2, B = 20
Sufficient.

B?
Intern
Intern
avatar
Joined: 07 Aug 2004
Posts: 20
Followers: 0

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

 [#permalink] New post 20 Aug 2004, 00:08
It is clear that statement (2) by itself is sufficient.
What about statement (1)?
It is possible to know X and Y if you have the values of XY and X-Y. Let's take C=-A.
We have AC=-40 and A+C=18
A and C are solutions of X²-(A+C)X+AC=0, ie, X²+40X+18=0. Thus, we can obtain A and C, A and B and calculate AB(A+2B).
What is the problem with this since the correct solution is B???

PS: Following my point of view, the answer is C
Manager
Manager
avatar
Joined: 02 Apr 2004
Posts: 224
Location: Utrecht
Followers: 1

Kudos [?]: 7 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Aug 2004, 01:41
I believe the answer is C

St1.

A - B = -18

-20 - - 2 = -18 or
2 - 20 = -18

A = -20 or 2
B = -2 or 20

Which will give different solutions

St2.

A = 2 or -2
B = 20

Which will give different solutions

Combined statements will say A = 2 and B = 20

Correct me if I am wrong.

Regards,

Alex
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 466
Followers: 1

Kudos [?]: 26 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Aug 2004, 06:32
kpinvictus wrote:
It is clear that statement (2) by itself is sufficient.
What about statement (1)?
It is possible to know X and Y if you have the values of XY and X-Y. Let's take C=-A.
We have AC=-40 and A+C=18
A and C are solutions of X²-(A+C)X+AC=0, ie, X²+40X+18=0. Thus, we can obtain A and C, A and B and calculate AB(A+2B).
What is the problem with this since the correct solution is B???

PS: Following my point of view, the answer is C


if you've already written that statement 2 by itself is sufficient, then you have to choose B. B always over-rides C.

Alex_NL wrote:
A = 2 or -2
B = 20

Which will give different solutions

Combined statements will say A = 2 and B = 20

Correct me if I am wrong.


A could be 2 or -2, but only 2 will work with 20 to make 80, so it has to be the positive version.
Manager
Manager
avatar
Joined: 02 Apr 2004
Posts: 224
Location: Utrecht
Followers: 1

Kudos [?]: 7 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Aug 2004, 07:29
What a stupid mistake I have made.

That is my problem sometimes. I dont read the question well.

:oops: :oops: :oops: :oops:
Director
Director
avatar
Joined: 20 Jul 2004
Posts: 593
Followers: 1

Kudos [?]: 22 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Aug 2004, 07:34
Alex_NL wrote:
What a stupid mistake I have made.

That is my problem sometimes. I dont read the question well.

:oops: :oops: :oops: :oops:

I too had this problem. From what I heard/learnt, there is one easy solution for this disease - PRACTICE. :)
Intern
Intern
avatar
Joined: 07 Aug 2004
Posts: 20
Followers: 0

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

 [#permalink] New post 23 Aug 2004, 00:44
what do you think IAN?
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 466
Followers: 1

Kudos [?]: 26 [0], given: 0

GMAT Tests User
 [#permalink] New post 23 Aug 2004, 06:21
kpinvictus wrote:
what do you think IAN?


Oh, sorry, I didn't put my answer. It's B.

This is a great question because it exemplifies a common trick ont he GMAT. They want us to pick D. The question starts out with an equation with two variables, and if we've got two variables, then another equation should be enough to solve the problem.

But be weary of that. Always double check. When variables multiply by themselves, they square, and that often leads to 2 solutions and not enough information. In the first statement, that's what happens. If you solve for B, you get that it could be either 20 or -2. That means A could be either -20 or 2, and both solutions work in both equations. So not enough information.

2 let's us know that A^2B is 80. Since we already knew that AB is 40, the extra A must be a positive 2, so be must be a positive 20, and that's sufficient.

If you are looking for me to comment on your method for solving 1, I'm not sure I understand it. I think you've made it too difficult. Don't try to look for sophisticated solutions on most problems. The GMAT won't ask you to do the kind of thing you did. If you're already comfortable with substitution to the point where you're changing variables around, then just do the substitution and see logically if it makes sense that there could be two different answers. If yes, then there's not enough information to solve the problem.
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 466
Followers: 1

Kudos [?]: 26 [0], given: 0

GMAT Tests User
 [#permalink] New post 23 Aug 2004, 07:06
by the way, kpinvictus, how did you get the square to come up in your problem? I'd love to know, because I hate typing that little "^" every time.
  [#permalink] 23 Aug 2004, 07:06
    Similar topics Author Replies Last post
Similar
Topics:
4 If ({a^1/2}*{b^1/3})^6=2000, what is the value of ab? madhavsrinivas 3 23 Dec 2013, 10:18
What is the value of ab^2 1. a = b-1 2. a = b^2-1 restore 3 21 Aug 2011, 14:19
If ab = -9, what is the value of ab(a + b) ? (1) a - b = 100 zisis 4 29 Aug 2010, 05:05
What is he maximum value of a/b? 1. a, a + b and a + 2b are meghash3 5 28 May 2010, 08:39
What is the value of a^4 - b^4 ? 1) a^2 - b^2 = 16 2) a+b = dorilee6 2 22 Dec 2006, 08:20
Display posts from previous: Sort by

If AB = 40, what is the value of AB(A + 2B)? (1) A ? B =

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.