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Good DS question...

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by The Jock » Mon Sep 06, 2010 7:52 am
What is the value of x?

(1) square root of x^4 = 9

(2) square root of x^2 = -x

x could be negative or 0 from stmt. 2. we have x= -3,3 from stmt. 1.
can we say that both stmt. sufficient.
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Varun
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Source: — Data Sufficiency |
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by selango » Mon Sep 06, 2010 8:04 am
stmt1,

sqrt(x^4)=9

-->x^4=81

But x can be 3 or -3.

Insuff

stmt2,

sqrt(x^2)=-x

-->x<0.but we don't know value of x

Insuff

Combining 1 and 2

Since x<0 x=-3

Pick C
--Anand--
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by Maciek » Mon Sep 06, 2010 8:08 am
Hi!

(1)
√(x^4) = 9
(x^4)^0.5 = 9
x^(4*0.5) = 9
x^2 = 9
either x = -3 or x = 3
Statement (1) ALONE is INSUFFICIENT
We should eliminate answers A and D

(2)
√(x^2) = -x
|x| = -x
|x| must be greater than 0
either x < 0 or x = 0
Statement (2) ALONE is INSUFFICIENT
We should eliminate answer B

(1) & (2)
x^2 = 9 & |x| = -x
(either x = -3 or x = 3) & (either x < 0 or x = 0)
Therefore, x = -3
We should eliminate answer E and choose answer C
Statements (1) and (2) both are TOGETHER SUFFICIENT

Hope it helps!
Best,
Maciek
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by The Jock » Mon Sep 06, 2010 8:43 am
Thanks a lot guys, I got it now....
Thanks and Regards,
Varun
https://mbayogi.wordpress.com/
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