inequality

cubicle_bound_misfit: Master | Next Rank: 500 Posts; Posts: 246; Joined: Mon May 19, 2008 7:34 am; Location: Texaco Gas Station; Thanked: 7 times

by cubicle_bound_misfit » Wed Jul 23, 2008 6:54 am

IMO it is B.

Please let me know OA.

my approach.
We gotta prove is x-y>x+y ?

i.e. is -y>y

stmt 2 SUFF.

regards,

Cubicle Bound Misfit

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jsl: Master | Next Rank: 500 Posts; Posts: 203; Joined: Wed Jun 04, 2008 1:01 am; Location: Windsor; Thanked: 5 times; GMAT Score:650

by jsl » Wed Jul 23, 2008 7:28 am

cubicle_bound_misfit wrote:We gotta prove is x-y>x+y

When you multiply an inequality, you need to be certain of the sign. If x+y is negative, the sign is reversed.... so I don't think you can do this since we can't be sure of the sign.

Would be interested in the OA though. I need a methodical way of working this one out!

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nikhilagrawal: Senior | Next Rank: 100 Posts; Posts: 81; Joined: Thu Jun 12, 2008 1:57 pm; Thanked: 1 times

by nikhilagrawal » Wed Jul 23, 2008 9:56 am

I think "cubicle_bound_misfit" i correct in solving the eqn.
The eqn can be reduced to 2y < 0 or y <0

so answer shld be B .

Pls correct me if I am going fundamentally wrong in soloving the equation.

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Canman: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Jul 11, 2008 5:00 am; Thanked: 4 times

by Canman » Wed Jul 23, 2008 11:23 am

I think jsl brings up a good point to remember about signs and direction of inequality when cross multiplying. But I also agree with some of the other posters and think B is sufficient.

To simplify the "rephrase" of the questions stem asks: "Is y>0 or is y<0?" (factoring in that the unknown signs can flip the inequality)

1) tells us nothing about y - insufficient
2) tells us y<0 - SUFFICIENT

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cubicle_bound_misfit: Master | Next Rank: 500 Posts; Posts: 246; Joined: Mon May 19, 2008 7:34 am; Location: Texaco Gas Station; Thanked: 7 times

by cubicle_bound_misfit » Wed Jul 23, 2008 11:27 am

hi JSL,

the way I tried it

if x-y/x+y is > 1 then both denominator and numerator both has to be either greater than zero or less than zero.

in both the cases if you pick numbers , multiplying expression by denominator does not invert ineqalities.

Please let me know if I am wrong and what's the OA?

regards,

Cubicle Bound Misfit

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Canman: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Jul 11, 2008 5:00 am; Thanked: 4 times

by Canman » Wed Jul 23, 2008 12:04 pm

Actually I'm rethinking this going back through it with a common sense check by picking some numbers... maybe I've overthought the problem by trying to solve it with algebra

Maybe 2) y<0 isn't so sufficient after all.

Consider x=3, y=-1
Stem eqn will equal 2 which is a "YES" answer

Consider x=3, y=-4
Stem eqn will equal -1 which is a "NO" answer

Statement 1) suffers the same conclusion, as well as the statements together.

Could E be the answer after all?

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Canman: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Jul 11, 2008 5:00 am; Thanked: 4 times

by Canman » Thu Jul 24, 2008 4:55 am

I checked and the OA on this is E.

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