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

It is currently 17 Sep 2014, 05:49

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>0, does (a+2)(b+2) = 4? (1) ab = -2(a+b) (2) a=b

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
avatar
Joined: 27 Aug 2005
Posts: 332
Location: Montreal, Canada
Followers: 2

Kudos [?]: 9 [0], given: 0

GMAT Tests User
If ab>0, does (a+2)(b+2) = 4? (1) ab = -2(a+b) (2) a=b [#permalink] New post 10 Sep 2005, 14:06
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

100% (01:54) correct 0% (00:00) wrong based on 3 sessions
If ab>0, does (a+2)(b+2) = 4?

(1) ab = -2(a+b)
(2) a=b

(Never mind, I realize what I did wrong...)
Senior Manager
Senior Manager
avatar
Joined: 27 Aug 2005
Posts: 332
Location: Montreal, Canada
Followers: 2

Kudos [?]: 9 [0], given: 0

GMAT Tests User
 [#permalink] New post 10 Sep 2005, 15:45
Yeah, OA is A.

I of course went through a whole elaborate solve method for B in which I assumed the solution while trying to determine it. Bad idea. :oops:
Current Student
avatar
Joined: 28 Dec 2004
Posts: 3404
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 13

Kudos [?]: 159 [0], given: 2

GMAT Tests User
 [#permalink] New post 02 Oct 2005, 12:24
why is it A?

Always attempt to give an explanation if you can....just so people can learn from it...

here is how I was thinking....

If ab>0, does (a+2)(b+2) = 4?

(1) ab = -2(a+b)
(2) a=b

so I re-arrange the stem (a+b)(4)=4...

so we need to know is if (a+b)=1

(1) says ab=-2(a+b)

then (we know ab>0) -ab/2=(a+b) or -1/2=[(a+b)/ab]...clearly (a+b) is not equal to 1...so (1) is sufficient...

(2) a=b
we know that a=b, well we really need to know if a=1 or 1/2 or b=1 or 1/2...this doesnt say much about a or b....so Insufficient...
Manager
Manager
avatar
Joined: 15 Jul 2005
Posts: 106
Followers: 1

Kudos [?]: 4 [0], given: 0

 [#permalink] New post 02 Oct 2005, 13:56
fresinha12 wrote:

so I re-arrange the stem (a+b)(4)=4...



how did you re-arrange (a+2)(b+2)=4 to (a+b)(4)=4?

Am I missing something?

I choose (D) (though I see the OA mentioned as A)


stem asks whether (a+2)(b+2)=4?

this can be re-arranged to ab+2a+2b=0

statement I: ab=-2(a+b), which can be rewritten to ab+2a+2b=0, thus sufficient.

statement II: a=b. is (a+2)(a+2)=4? (a+2)^2=4, or a+2=+2 or -2, therefore a = -4, since if a+2=+2, a would equal zero, and ab would not be > 0. since a = b, a = b = -4. therefore (-4+2)(-4+2)=4. Sufficient.
Senior Manager
Senior Manager
avatar
Joined: 30 Oct 2004
Posts: 289
Followers: 1

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

GMAT Tests User
 [#permalink] New post 02 Oct 2005, 14:06
Chets, can you explain how we can just solve the equation (a+2)(b+2) = 4 when the stem says we are not sure if (a+2)(b+2) is indeed 4.
From 2) all you really get is (a+2)(a+2) which is (a+2)^2.. .which does not mean that the eqn is necessarily = 4. a can be anything.... 1,2, -5, 3/4, Depending on what value of a you select ... (a+2)^2 can have any value. So insufficient. All it means is that for the condition to be true, we need a=2 and a=b does not tell you that.
_________________

-Vikram

Manager
Manager
avatar
Joined: 15 Jul 2005
Posts: 106
Followers: 1

Kudos [?]: 4 [0], given: 0

 [#permalink] New post 02 Oct 2005, 15:11
vikramm wrote:
Chets, can you explain how we can just solve the equation (a+2)(b+2) = 4 when the stem says we are not sure if (a+2)(b+2) is indeed 4.
From 2) all you really get is (a+2)(a+2) which is (a+2)^2.. .which does not mean that the eqn is necessarily = 4. a can be anything.... 1,2, -5, 3/4, Depending on what value of a you select ... (a+2)^2 can have any value. So insufficient. All it means is that for the condition to be true, we need a=2 and a=b does not tell you that.


Good call, statement II doesn't suffice. So I guess A it is!
Manager
Manager
avatar
Joined: 25 Aug 2004
Posts: 171
Location: MONTREAL
Followers: 1

Kudos [?]: 5 [0], given: 0

 [#permalink] New post 02 Oct 2005, 16:20
It is A,

Probably a question asked at the end of a GMAT exam. Possibility that it is an experimental question...
Senior Manager
Senior Manager
User avatar
Joined: 14 Apr 2005
Posts: 422
Location: India, Chennai
Followers: 1

Kudos [?]: 3 [0], given: 0

GMAT Tests User
Re: DS - never mind, I realize what I did wrong [#permalink] New post 03 Oct 2005, 02:01
coffeeloverfreak wrote:
If ab>0, does (a+2)(b+2) = 4?

(1) ab = -2(a+b)
(2) a=b

(Never mind, I realize what I did wrong...)


My answer is A. Here is the explanation.

(a+2) (b+2) = ab + 2a + 2b + 4
=> ab + 2(a+b) + 4

From statement 1 we have ab = -2(a+b), substituting in above equn,
-2(a+b) + 2(a+b) + 4
= 4 , So A is sufficient to answer the solution.

From statement 2, we get a = b applying this in original equn we get
a^2+4+4a , here the value will differ for every value of A. Hence B is not sufficient.

Thanks
Sreeni
Re: DS - never mind, I realize what I did wrong   [#permalink] 03 Oct 2005, 02:01
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic If ab > 0, does (a - 2)(b - 2) = 4 ? WoundedTiger 4 15 Aug 2013, 01:22
Is (A/B)^3<(AB)^3 1) A>0 2) AB>0 DeeptiM 6 05 Sep 2011, 01:18
(a^3)b+(a^2)(b^2)+a(b^3)>0? 1. ab>0 2. b<0 Creeper300 4 05 Nov 2010, 08:43
If ab does not = 0 and a^2*b^2-ab= 6, which of the following positive soul 4 25 Jun 2006, 01:12
If a + b = a^2 - b^2 and ab > 0, which of the following sandalphon 4 20 Dec 2005, 08:09
Display posts from previous: Sort by

If ab>0, does (a+2)(b+2) = 4? (1) ab = -2(a+b) (2) a=b

  Question banks Downloads My Bookmarks Reviews Important topics  


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®.