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## Source Grockit: DS: Inequallity

tagged by: polter

This topic has 1 expert reply and 3 member replies
polter Just gettin' started!
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Source Grockit: DS: Inequallity Wed Apr 25, 2012 7:27 pm
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
If m ≠ -n, is (m-n)/(m+n)> 1?

(1) n < 0

(2) m > 0

[spoiler]E[/spoiler]

I think the correct answer should be different.

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shantanu86 Rising GMAT Star
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Wed Apr 25, 2012 8:39 pm
polter wrote:
If m ≠ -n, is (m-n)/(m+n)> 1?

(1) n < 0

(2) m > 0

E

I think the correct answer should be different.
Hi polter,

Pls go th. http://www.beatthegmat.com/fast-way-to-do-this-t110788.html#467098

Regards,
Shantanu

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spartacus1412 Really wants to Beat The GMAT!
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Wed Apr 25, 2012 8:41 pm
the question says m +n =0 (given m!= -n)
to find if (m-n)/(m+n)> 1?

this can be reduced to (m-n)/(m+n) -1 >0
i.e. -2n/(m+n)>0

option1: n<0
we cannot say anything about the sign of m+n. hence, above expression can be + as well as -
hence, insufficient.

option1: m>0
we cannot say anything about the sign of above expression. hence, above expression can be + as well as -
hence, insufficient.

combine both : n<0 and m>0
the above expression wil be less than zero only if abs(n)> abs(m), which is not given.

hence, both together are insufficient.

Hope it Helps

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polter Just gettin' started!
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Sun Apr 29, 2012 11:31 am
Hi shantanu86/ spartacus1412, thank you for your suggestions.

My confusion was with this: can this expression not be reduced as
(m-n)/(m+n)> 1
=> (m-n)> (m+n)
=> -n > n
=> 0 > 2n
=> 0 > n

Since (1) clearly defines this. Hence A

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Stuart Kovinsky GMAT Instructor
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Sun Apr 29, 2012 1:43 pm
polter wrote:
Hi shantanu86/ spartacus1412, thank you for your suggestions.

My confusion was with this: can this expression not be reduced as
(m-n)/(m+n)> 1
=> (m-n)> (m+n)
=> -n > n
=> 0 > 2n
=> 0 > n

Since (1) clearly defines this. Hence A
Hi!

Whenever you see inequalities and variables, alarm bells should go off in your head and your internal warning system should be shouting "DANGER DANGER DANGER!!!"

Remember this key difference between equations and inequalities:

When you multiply or divide both sides of an inequality by a negative number, you flip the inequality.

With that rule in mind, here's the mistake you made: you divided both sides by (m+n) without knowing whether that term was positive or negative.

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www.kaptest.com

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