Some questions from GMAT Prep - please help

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aim-wsc
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Tue Mar 27, 2007 1:03 pm

momentary_lapse wrote: 2) Data Sufficiency: Is 1/p > r/(r^2 + 2) 1) p=r 2) r=0 1) p=r is insufficient: reason +ve, -ve values... 2)r=0 insufficient: reason NO info about p together: statement two (supports statement 1 &) tells about the exact sign of r and hence of p if related with statement 1. let me explain it once again. given equation if cross multiplied: (r^2+2) > pr Now p=r=0 2>0 gotcha 8) ANSWER C therefore _________________ Getting started @BTG? Beginner's Guide to GMAT \| Johny learns to blog Please do not PM me, (not active anymore) contact Eric.

momentary_lapse
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Wed Mar 28, 2007 2:09 am

aim, thanks.. how is -x = -1 * x'? if x<0 wont -x = -1 * x = x' ?

gabriel
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Wed Mar 28, 2007 3:26 am

aim-wsc wrote: first off: \|x\| CANNOT BE equal to -x (never) now -x\|x\| = (-1)* (x) * mod (x).............(remember x has -ve value already! since x<0) so let x= (-1)* x' where x'= (+ve) x =(-1)* (-1)x' * x' = (-1)^2 * x'^2 I think it is very easy to sq rooting above value. which equals to =(-1)* x' =-x ... in my own verbally challenged way this is exactly what i was tryin to explain.... may be i shuld try and avoid all those stupid jargon in the future... nywayz the explanation provided is one way at looking at the answer to the q...

aim-wsc
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Wed Mar 28, 2007 5:07 am

momentary_lapse wrote: aim, thanks.. how is -x = -1 * x'? if x<0 wont -x = -1 * x = x' ? I took x' as +ve sign of x. ... just to explain it i used the term, its not a std notation btw. _________________ Getting started @BTG? Beginner's Guide to GMAT \| Johny learns to blog Please do not PM me, (not active anymore) contact Eric.

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Stacey Koprince
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Mon Apr 16, 2007 11:28 pm

Quote: 1) If x<0 , what is square root of -x\|x\| And answer choices are: Quote: -x,x,1,0 and square root of x Given x<0: -x is a positive number. \|x\| is a positive number Therefore, we can simplify the expression "-x\|x\|" as x^2. The square root of x^2 = the positive and negative values of the given variable (x). We were told initially that x<0, so the only valid root is the negative one, or -x. This is a confusing question because, in the beginning, we interpret "-x" to be a positive number, since we know x is negative. And then, at the end, we use that same "-x" to mean the negative value of the number. Looks the same - but it isn't. Try it with real numbers x < 0. SQRT - (-2)\|-2\| = SQRT 22 = SQRT 4 = +/- 2 If x is negative, then only -2 is the valid root. See, with these number, how the first "-x" [-(-2)] isn't the same thing as the second "-x" [-2]? _________________ Stacey Koprince GMAT Instructor Director of Online Community Manhattan GMAT Contributor to Beat The GMAT! Learn more about me

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Stacey Koprince
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Mon Apr 16, 2007 11:32 pm

As Gabriel noted, the second problem has been transcribed incorrectly. Quote: ) Data Sufficiency: Is 1/p > r/(r^2 + 2) 1) p=r 2) r=0 The second statement should read "r>0." Which changes everything. I'll let you guys play with it now (note that this is a REALLY hard question - so don't feel badly if it's giving you fits!) - you can find the correct answer in OG11 #145. _________________ Stacey Koprince GMAT Instructor Director of Online Community Manhattan GMAT Contributor to Beat The GMAT! Learn more about me