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

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Is ab = 1 ? (1) aba = a (2) bab = b [#permalink] New post 21 Aug 2008, 06:36
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C
D
E

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

please explain your answer.

thanks
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Re: DS tricky quesiton [#permalink] New post 21 Aug 2008, 07:02
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elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

please explain your answer.

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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Re: DS tricky quesiton [#permalink] New post 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
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Re: DS tricky quesiton [#permalink] New post 21 Aug 2008, 07:37
x2suresh wrote:
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

please explain your answer.

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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 18 Oct 2008, 02:09
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my answer is c

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

thus the answer is c
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Re: DS tricky quesiton [#permalink] New post 18 Oct 2008, 02:24
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

please explain your answer.

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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 18 Oct 2008, 23:35
elmagnifico wrote:
Is ab = 1 ?
(1) aba = a
(2) bab = b

please explain your answer.

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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 21 Oct 2008, 06:37
Lol, the answers are all over the place. :lol:

Can someone give the OA please.
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Re: DS tricky quesiton [#permalink] New post 21 Oct 2008, 16:21
Here it is 59-p526795
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Re: DS tricky quesiton [#permalink] New post 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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Re: DS tricky quesiton [#permalink] New post 22 Oct 2008, 07:04
bigfernhead 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 ....
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Re: DS tricky quesiton [#permalink] New post 22 Oct 2008, 07:11
Ahh! Yes! Thanks

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amitdgr wrote:
bigfernhead 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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