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kplan _DS2

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shinewine
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kplan _DS2 [#permalink] New post   26 Aug 2006, 07:37
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Please try this questoin.. givethe xplanation also



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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 09:47
(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

(2) We get a^2/(a-6)=-8
So a^2+8a-48=0
(a+12)(a-4)=0

a is either -12 or 4 NOT SUFF
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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 10:49
kevincan wrote:
(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

(2) We get a^2/(a-6)=-8
So a^2+8a-48=0
(a+12)(a-4)=0

a is either -12 or 4 NOT SUFF


Kevin, how do you know that a can't be -4 in statement 1?
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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 10:53
GMATT73 wrote:
kevincan wrote:
(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

(2) We get a^2/(a-6)=-8
So a^2+8a-48=0
(a+12)(a-4)=0

a is either -12 or 4 NOT SUFF


Kevin, how do you know that a can't be -4 in statement 1?


a^2/a=a , not |a|

Notice that if a=-4, from question b=-2

But if a=-4, from (1), b=2
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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 11:04
kevincan wrote:
GMATT73 wrote:
kevincan wrote:
(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

(2) We get a^2/(a-6)=-8
So a^2+8a-48=0
(a+12)(a-4)=0

a is either -12 or 4 NOT SUFF


Kevin, how do you know that a can't be -4 in statement 1?


a^2/a=a , not |a|

Notice that if a=-4, from question b=-2

But if a=-4, from (1), b=2


Yes, of course. b must be negative for the original question to hold.
I wish I had had you as my Kaplan instructor last year :oops:
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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 11:15
Got the same result as kevincan

For ST1, a=4, b=-2 SUFF

For ST2, a=12 or a=-4 NOTSUFF
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Re: kplan _DS2 [#permalink] New post   26 Aug 2006, 18:43
kevincan wrote:
(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

(2) We get a^2/(a-6)=-8
So a^2+8a-48=0
(a+12)(a-4)=0

a is either -12 or 4 NOT SUFF


(1) a^2/b=-8 and b/a= -1/2

Multiplying , we get a=4 and thus b=-2 SUFF

Can you explain how you arrived at the answer?
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Re: kplan _DS2 [#permalink] New post   27 Aug 2006, 00:01
shinewine wrote:
Please try this questoin.. givethe xplanation also


a^2/b = -8
a(a-b) = ?

(1) a = -2b

From Qstem a^2= -8b
sub(1) in Qstem a^2 = 4(-2b)
a^2 = 4a
a^2-4a=0
a(a-4)=0
a=0 or 4
Hence b=0 or -2

We will get a(a-b) = 0 or 24 Insuff
BCE

(2) a-b=6
a=6+b
Qstem :a^2= -8b
sub (2) in Qstem
(6+b)^2 = -8b
36+b^2+12b= -8b
b^2+20b+36=0
(b+18)(b+2)=0
b=-18 or -2
Hence a = -12 or 4
Hence a(a-b) = -72 or 24
CE

(1) &(2)
a=4 b= -2 Hence a(a-b) = 24

Hence C

What is the source of this Q?

Heman
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Re: kplan _DS2 [#permalink] New post   27 Aug 2006, 00:08
heman wrote:
shinewine wrote:
Please try this questoin.. givethe xplanation also


a^2/b = -8
a(a-b) = ?

(1) a = -2b

From Qstem a^2= -8b
sub(1) in Qstem a^2 = 4(-2b)
a^2 = 4a
a^2-4a=0
a(a-4)=0
a=0 or 4
Hence b=0 or -2

We will get a(a-b) = 0 or 24 Insuff
BCE


Heman


I see my mistake in (1) a=0 b=0 cannot hold since a/b will be indeterminate in Gmat land. Hence only possible value of a=4
Suff

A

Heman



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Re: kplan _DS2 [#permalink]
27 Aug 2006, 00:08
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