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

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Manager
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Is ab = 1 ? (1) aba = a (2) bab = b [#permalink]

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21 Aug 2008, 06:36
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Is ab = 1 ?
(1) aba = a
(2) bab = b

thanks
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21 Aug 2008, 07:02
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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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21 Aug 2008, 07:08
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
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21 Aug 2008, 07:37
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??
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21 Aug 2008, 07:42
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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18 Oct 2008, 02:09
1
KUDOS

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

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18 Oct 2008, 02:24
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
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18 Oct 2008, 07:45
gmat usually says a and b are different from 0 or something like that

in this case

E
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18 Oct 2008, 23:35
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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Its Now Or Never

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20 Oct 2008, 04:43
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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20 Oct 2008, 14:07
I got C as well, since Ab = 1 is common for both of the answers.

What's the OA?
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20 Oct 2008, 22:56
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
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20 Oct 2008, 23:59
My ans is E.

After simplification,
(1) ab = 1 if a is not '0'.
(2) ab = 1 if b is not '0'.
Therefore (E).
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21 Oct 2008, 06:11
(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
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21 Oct 2008, 06:37
Lol, the answers are all over the place.

Can someone give the OA please.
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21 Oct 2008, 16:21
Here it is 59-p526795
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22 Oct 2008, 05:43
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?
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22 Oct 2008, 07:04
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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22 Oct 2008, 07:11
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 ....
Re: DS tricky quesiton   [#permalink] 22 Oct 2008, 07:11
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