GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 18 Jun 2018, 08:43

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

What is the value of a + b? (1) a^2 + b^2 = 13 (2) 2b = 12/a

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
avatar
Joined: 16 Oct 2008
Posts: 54
What is the value of a + b? (1) a^2 + b^2 = 13 (2) 2b = 12/a [#permalink]

Show Tags

New post 17 Nov 2008, 02:02
What is the value of a + b?
(1) a^2 + b^2 = 13
(2) 2b = 12/a

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Director
Director
avatar
Joined: 14 Aug 2007
Posts: 697
Re: No. prop Q [#permalink]

Show Tags

New post 17 Nov 2008, 02:09
Natasha0123 wrote:
What is the value of a + b?
(1) a^2 + b^2 = 13
(2) 2b = 12/a


1,2 are individually insuff .

together we have

a^2+2ab+b^2= 13 + 2ab
(a+b)^2 = 15
a+b = sqrt(15)

C
Manager
Manager
avatar
Joined: 30 Sep 2008
Posts: 111
Re: No. prop Q [#permalink]

Show Tags

New post 17 Nov 2008, 02:13
(1) & (2)

a^2 + b^2 = (a+b)^2 - 2ab = 13

=> (a+b)^2 = 13 + 2ab = 13 + 2*6 = 25

=> a + b = 5 or a + b = -5

E
Director
Director
avatar
Joined: 14 Aug 2007
Posts: 697
Re: No. prop Q [#permalink]

Show Tags

New post 17 Nov 2008, 02:32
Natasha0123 wrote:
alpha_plus_gamma wrote:
Natasha0123 wrote:
What is the value of a + b?
(1) a^2 + b^2 = 13
(2) 2b = 12/a


1,2 are individually insuff .

together we have

a^2+2ab+b^2= 13 + 2ab
(a+b)^2 = 15
a+b = sqrt(15)

C


why 13 + 2ab = 15?


Oh sorry that was typo, i meant 13+12=25
Intern
Intern
avatar
Joined: 25 Mar 2008
Posts: 43
Re: No. prop Q [#permalink]

Show Tags

New post 20 Nov 2008, 23:32
whats the OA for this ?

is it C ?

GMAT does not support negative square root.

please post the OA.

thanks
Manager
Manager
avatar
Joined: 02 Nov 2008
Posts: 56
Re: No. prop Q [#permalink]

Show Tags

New post 21 Nov 2008, 09:39
I would go with E. Don't know if a+b = -5 or +5
Retired Moderator
User avatar
B
Joined: 05 Jul 2006
Posts: 1734
GMAT ToolKit User Premium Member
Re: No. prop Q [#permalink]

Show Tags

New post 22 Nov 2008, 08:01
Natasha0123 wrote:
What is the value of a + b?
(1) a^2 + b^2 = 13
(2) 2b = 12/a


EACH ALONE IS INSUFF

both

add them

a^2+b^2+2ab = 25 ie: (a+b)^2 = 25

a+b can either 5 or -5............E
Manager
Manager
avatar
Joined: 16 Oct 2008
Posts: 54
Re: No. prop Q [#permalink]

Show Tags

New post 26 Nov 2008, 04:14
I also pick E but OA is C

c. Remember that (a + b)2 = a2 + 2ab + b2. From statement (1), we know that a2 + b2 = 13. By crossmultiplying
in statement (2), we get 2ab = 12. Since we know the values of a2 + b2 and 2ab, and
(a + b)2 = a2 + 2ab + b2, we can now take the square root of the sum to find the value of a + b.

source : Gmat Exam Success book
VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1340
Re: No. prop Q [#permalink]

Show Tags

New post 26 Nov 2008, 15:06
If a book says OA is C, The book you are working on has serious issues.

I got E because a+b can be 5 or -5
Manager
Manager
avatar
Joined: 27 May 2008
Posts: 193
Re: No. prop Q [#permalink]

Show Tags

New post 27 Nov 2008, 23:42
you are absolutely correct icandy
VP
VP
avatar
Joined: 17 Jun 2008
Posts: 1479
Re: No. prop Q [#permalink]

Show Tags

New post 28 Nov 2008, 04:45
yes, OA must be E (unless the question stem says that a and b are positive, or negative, etc.).

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: No. prop Q   [#permalink] 28 Nov 2008, 04:45
Display posts from previous: Sort by

What is the value of a + b? (1) a^2 + b^2 = 13 (2) 2b = 12/a

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.