Last visit was: 19 Nov 2025, 11:40 It is currently 19 Nov 2025, 11:40
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
User avatar
pb_india
User avatar
Joined: 10 Dec 2004
Last visit: 27 May 2005
Posts: 173
Own Kudos:
1,338
Posts: 173
Kudos: 1,338
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 02 Feb 2005, 10:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
N
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

History

Date
Time
Result
Not Attempted Yet
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater?
1) a=2b
2) a+b>1



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Data Sufficiency (DS) Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
User avatar
MA
User avatar
Joined: 25 Nov 2004
Last visit: 09 Aug 2011
Posts: 697
Own Kudos:
515
Posts: 697
Kudos: 515
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 02 Feb 2005, 22:44
Kudos
Add Kudos
Bookmarks
Bookmark this Post
pb_india
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater?
1) a=2b
2) a+b>1
Show more


(a^-1+b^-1)^-1 =>ab/(a+b)
(a^-1*b^-1)^-1 => ab

1) a=2b => not sufficient.

2) a+b>1 => not sufficient.

togather also insufff...........
avatar
HongHu
avatar
Joined: 03 Jan 2005
Last visit: 25 Apr 2011
Posts: 966
Own Kudos:
796
Posts: 966
Kudos: 796
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 03 Feb 2005, 10:04
Kudos
Add Kudos
Bookmarks
Bookmark this Post
1/a+1/b=(a+b)/ab
S=(1/a+1/b)-1/ab=1/ab*(a+b-1)

(I) a=2b
S=1/2b^2*(3b-1) depending on b's value. insufficient
(II) a+b>1
a+b-1>0
depending on the signs of a and b
Combine
2b^2>0
a+b-1>0
S>0
Sufficient

(C)
User avatar
banerjeea_98
User avatar
Joined: 18 Nov 2004
Last visit: 17 May 2012
Posts: 676
Own Kudos:
201
Posts: 676
Kudos: 201
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? Updated on: 03 Feb 2005, 10:27
Originally posted by banerjeea_98 on 03 Feb 2005, 10:18.
Last edited by banerjeea_98 on 03 Feb 2005, 10:27, edited 1 time in total.
Kudos
Add Kudos
Bookmarks
Bookmark this Post
EDITED

"C".....altho I am assuming from the eqn that a and b <> 0...as it will make 1/b or 1/a...infinity,
now....we have ab/a+b and ab as 2 eqn

I....if a = 2b....then.....first one becomes 2b/3 and second is 2b^2.....if b < 0....then 2nd one is > ....if b
is >=1....then 2nd is >....if 0<b<1....say b = 1/4.....then first is >....so insuff

II...if a+b > 1.....first ab/a+b is always < than ab, if ab is +ve and > ab is ab is -ve...so insuff...


Combine
a = 2b and a+b > 1
b > 1/3....so b +ve......and a is +ve.....so from II.....we get ab/a+b < ab...suff
avatar
HongHu
avatar
Joined: 03 Jan 2005
Last visit: 25 Apr 2011
Posts: 966
Own Kudos:
796
Posts: 966
Kudos: 796
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 03 Feb 2005, 10:25
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ab could be a negative number, baner.
User avatar
banerjeea_98
User avatar
Joined: 18 Nov 2004
Last visit: 17 May 2012
Posts: 676
Own Kudos:
201
Posts: 676
Kudos: 201
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 03 Feb 2005, 10:31
Kudos
Add Kudos
Bookmarks
Bookmark this Post
HongHu
ab could be a negative number, baner.
Show more

Yep...I realized it as soon as I had hit the submit, I edited my post.... :oops:
User avatar
MA
User avatar
Joined: 25 Nov 2004
Last visit: 09 Aug 2011
Posts: 697
Own Kudos:
515
Posts: 697
Kudos: 515
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 04 Feb 2005, 00:12
Kudos
Add Kudos
Bookmarks
Bookmark this Post
HongHu
ab could be a negative number, baner.
Show more



explain pls......... i believe from i and ii, ab cannot be a -ve.
avatar
HongHu
avatar
Joined: 03 Jan 2005
Last visit: 25 Apr 2011
Posts: 966
Own Kudos:
796
Posts: 966
Kudos: 796
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 04 Feb 2005, 00:28
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Sorry, was responding to baner's post before he edited it. ab could be negative for (II).
User avatar
Folaa3
User avatar
Joined: 27 Dec 2004
Last visit: 14 Apr 2006
Posts: 382
Own Kudos:
128
Posts: 382
Kudos: 128
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 04 Feb 2005, 06:46
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Can someone please explain how statement II is sufficient? I have tried all possible means and only statement I seems suffiicient
User avatar
anirban16
User avatar
Joined: 24 Jan 2005
Last visit: 20 Jun 2005
Posts: 141
Own Kudos:
68
Location: Boston
Posts: 141
Kudos: 68
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 04 Feb 2005, 08:50
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Question is ab/a+b > or < ab

(I) a=2b ==> ab is positive as a and b have the same sign. Now a+b could be either >1 or less than 1 so can't say. Eliminate A and D

(II) a+b>1. Don't say about the signs of a and b so ab could be either +ve or -ve. Can't compare. Eliminate B

Both (I) and (II) ==> ab>0 and a+b>0 so ofc ab/a+b < ab.

Answer is C

Thanks,

Anirban
avatar
HongHu
avatar
Joined: 03 Jan 2005
Last visit: 25 Apr 2011
Posts: 966
Own Kudos:
796
Posts: 966
Kudos: 796
Which one of (a^-1+b^-1)^-1 and (a^-1*b^-1)^-1 is greater? 04 Feb 2005, 10:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Folaa3
Can someone please explain how statement II is sufficient? I have tried all possible means and only statement I seems suffiicient
Show more


Both I and II are insufficient. But combining them is sufficient.



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Data Sufficiency (DS) Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
Moderators:
Bunuel
Math Expert
105390 posts
GMATBusters
GMAT Tutor
1924 posts