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Director
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DS..Explaination needed [#permalink]
 07 Jun 2007, 19:38
Question Stats:
0% (00:00) correct
 0% (00:00) wrong based on 0 sessions
Is A < 0 ?
1. -A = |-A|
2. A^2 = 9
Can someone please explain why the answer is C . I chose E.
Does the product of M and N equal to 1 ?
1. A*B*A = A
2. B*A*B = B
Why the answer is E. I chose D.
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Manager
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Is A < 0 ?
1. -A = |-A|
2. A^2 = 9
1)I think answer should be A
2) How is M & N related to A & B??Please make sure question is complete. thx
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Director
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Re: DS..Explaination needed [#permalink]
07 Jun 2007, 21:55
trahul4 wrote: Does the product of M and N equal to 1 ?
1. A*B*A = A
2. B*A*B = B
agree with E but i never saw such question in gmat. 
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Re: DS..Explaination needed [#permalink]
08 Jun 2007, 04:29
trahul4 wrote: Is A < 0 ?
1. -A = |-A|
2. A^2 = 9
Can someone please explain why the answer is C . I chose E.
Does the product of M and N equal to 1 ?
1. A*B*A = A
2. B*A*B = B
Why the answer is E. I chose D.
From (1)
A either 0 or a negative number - Alone not sufficient
From (2)
A either -3 or 3 - Alone not sufficient
From both statement we can say A = 3
So, my choice E
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Director
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1. -A =|-A|
A has to be negative
OR A could be zero, an integer that satisfies the condition above.
statement 1 is insufficient
2. A^2 = 9
-------------
Here either A is negative or positive.
statement 2 is insufficient
(1) and (2) together
-------------------------
A is either negative or zero from (1) and A is either negative or positive from (2) --> A is zero
Answer C
Last edited by Mishari on 08 Jun 2007, 09:26, edited 1 time in total.
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Director
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the second question .. please clarify .. A,B versus M and N ?
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Director
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Sorry for the typo mistake .. here it goes second question
Does the product of A and B equal to 1 ?
1. A*B*A = A
2. B*A*B = B
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Manager
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[quote="trahul4"]Sorry for the typo mistake .. here it goes second question
Does the product of A and B equal to 1 ?
1. A*B*A = A
2. B*A*B = B[/quote]\
Solution:
I would go for E;
Stmt1: A*B*A = A; this implies that B = 1 or B = 0 as (A^2 * B) = A ; but we don't know anything about A, so Insufficient
Stmt2: B*A*B = B; implies that A = 1 or A = 0 as (B^2 * A) = B; but we don't know anything about B from this statement, therefore insufficient
Stmt1 + Stmt2; Still insufficient because A*B could be 1 or 0
therefore, answer is E
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SVP
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Is A < 0 ?
1. -A = |-A|
2. A^2 = 9
---------------
(C) it is 
From 1
-A = |-A|
=> -A >= 0 as an absolute value is always positive or nul
<=> A =< 0 >>> We remain with the case of A = 0
INSUFF.
From 2
A^2 = 9
implies that
o A = 3 (> 0)
or
o A = -3 (< 0)
INSUFF.
Combining (1) & (2)
From 1, we know that A =< 0. That forces with what we know from 2 (A= +/- 3) A to be equal to -3.
SUFF.
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Director
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To find whether AxB = 1:
1. A*B*A = A
--------------------
A^2 x B = A --> B = 1/A and hence AxB = 1
OR A = 0 and thus AxB = 0
statement 1 is insufficient
2. B*A*B = B
-----------------
B^2 x A = B --> A = 1/B and hence AxB = 1
OR B = 0 and thus AxB = 0
A^2 x B = A --> B = 1/A
(1) and (2) together
------------------------
still insufficient as we have multiple cases or options
Answer: E
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