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# Is ab = 1 ? (1) aba = a (2) bab = b

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Manager
Joined: 12 Feb 2008
Posts: 176
Is ab = 1 ? (1) aba = a (2) bab = b [#permalink]

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21 Aug 2008, 07:36
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Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks

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

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SVP
Joined: 07 Nov 2007
Posts: 1733
Location: New York

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21 Aug 2008, 08:02
1
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks

(1) aba = a
aba-a=0 --> a(ab-1)=0
two solutions a=0 or ab=1
when a=0 ab=0 too.
Insufficient.

(2) bab = b
bab-b=0 b(ab-1)=0
b=0 or ab=1
when b=0 ab=0 too.
insufficient.

when you combine.
ab=1 a=0 b=0
so ab=1 or ab=0
insufficient

E.
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Joined: 28 Dec 2004
Posts: 3288
Location: New York City
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21 Aug 2008, 08:08
E for me too..ab=0 where a=0 b=0 is a possibility also ab=1 a=1 b=1 is also a possibility
Manager
Joined: 12 Feb 2008
Posts: 176

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21 Aug 2008, 08:37
x2suresh wrote:
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks

(1) aba = a
aba-a=0 --> a(ab-1)=0
two solutions a=0 or ab=1
when a=0 ab=0 too.
Insufficient.

(2) bab = b
bab-b=0 b(ab-1)=0
b=0 or ab=1
when b=0 ab=0 too.
insufficient.

when you combine.
ab=1 a=0 b=0
so ab=1 or ab=0
insufficient

E.

Why cant you just simply divide by a. this is not inequality, there is now sigh change??
SVP
Joined: 07 Nov 2007
Posts: 1733
Location: New York

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21 Aug 2008, 08:42
elmagnifico wrote:

Why cant you just simply divide by a. this is not inequality, there is now sigh change??

You can't do that.. If "a not equal 0" then you can simply divide with a.

say a=0 when you divide with 0 ----what is is value ?-- undefined..
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Manager
Joined: 28 Apr 2008
Posts: 110

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18 Oct 2008, 03:09
1

from 1 a could be 0- so ins

from 2- B could be 0- so ins

combined- a cant be o begaus of (2), B cant be 0 because of (1) so sufficient

Retired Moderator
Joined: 05 Jul 2006
Posts: 1734

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18 Oct 2008, 03:24
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks

is ab = 1

a( ab-1) = 0

thus either a = 0 or ab= 1 ie , a=b=-1 or a=b=1........insuff

from 2

b(ab-1) = 0
thus either b = 0 or ab= 1 ie , a=b=-1 or a=b=1........insuff

both together
ab = 1 suff

C
Senior Manager
Joined: 04 Aug 2008
Posts: 363

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18 Oct 2008, 08:45
gmat usually says a and b are different from 0 or something like that

in this case

E
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VP
Joined: 17 Jun 2008
Posts: 1285

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19 Oct 2008, 00:35
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks

Kindly post the OA

i get C

1) a=0 or ab=1
2)b=0 or ab=1

1) and 2) have commoin root ab=1 hence IMO C
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Manager
Joined: 04 Sep 2008
Posts: 233
Location: Kolkata
Schools: La Martiniere for Boys

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20 Oct 2008, 05:43
Why cant it be D

aba = a implies ab =1 as a cancels from both sides

Same with (2)

Correct me if I am wrong.
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Thanks
rampuria

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Joined: 18 Jul 2008
Posts: 898

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20 Oct 2008, 15:07
I got C as well, since Ab = 1 is common for both of the answers.

What's the OA?
Manager
Joined: 04 Sep 2008
Posts: 233
Location: Kolkata
Schools: La Martiniere for Boys

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20 Oct 2008, 23:56
Both a and b could be equal to Zero.

So we cannot really say whether ab=1 even when we combine the two equations.

Hence E
Manager
Joined: 21 May 2008
Posts: 83

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21 Oct 2008, 00:59
My ans is E.

After simplification,
(1) ab = 1 if a is not '0'.
(2) ab = 1 if b is not '0'.
Therefore (E).
Manager
Joined: 12 Oct 2008
Posts: 99

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21 Oct 2008, 07:11
(1) aba=a divide both sides of equation by a =>> ab=1 , because a/a=1 >>> suff
(2) bab=b divide both sides of equation by b=>> ab=1 >>>> suff

therefore, D
Retired Moderator
Joined: 18 Jul 2008
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21 Oct 2008, 07:37
Lol, the answers are all over the place.

Can someone give the OA please.
Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown

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21 Oct 2008, 17:21
Here it is 59-p526795
Retired Moderator
Joined: 18 Jul 2008
Posts: 898

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22 Oct 2008, 06:43
I picked C because AB =1 is common in both of the a) and b). Isn't that a logical reason why C should be the answer?
VP
Joined: 30 Jun 2008
Posts: 1007

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22 Oct 2008, 08:04
I picked C because AB =1 is common in both of the a) and b). Isn't that a logical reason why C should be the answer?

We have ab=0 also common for both the statements ....
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Retired Moderator
Joined: 18 Jul 2008
Posts: 898

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22 Oct 2008, 08:11
Ahh! Yes! Thanks

amitdgr wrote:
I picked C because AB =1 is common in both of the a) and b). Isn't that a logical reason why C should be the answer?

We have ab=0 also common for both the statements ....

--== 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: DS tricky quesiton   [#permalink] 22 Oct 2008, 08:11
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