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There was a prob with my calc the first time around. I've

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Director
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There was a prob with my calc the first time around. I've [#permalink] New post 01 Mar 2007, 23:14
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A
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C
D
E

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There was a prob with my calc the first time around. I've since corrected this prob.

if m>0 and n>0 is m+x/n+x > m/n?

stmnt 1: m is greater than n
stmnt 2: x is greater than 0

m+x/n+x > m/n =

m+x/n+x - m/n > 0 =

n(m+x)/n(n+x) - m(n+x)/n(n+x) > 0 = nm + nx - mn - mx/n^2 + nx =

nx - mx/n^2 + nx = -mx/n^2

Rephrased, the question reads: is -mx/n^2 > 0?

I picked b. The stem states that m and n are greater than 0. Statement 2 says that x is greater than 0. If m, n and x are all greater than 0 the equation must be greater than 0 too. The answer is C. Where did I go wrong?

Last edited by ggarr on 02 Mar 2007, 03:40, edited 5 times in total.
Manager
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 [#permalink] New post 02 Mar 2007, 02:27
I guess there is a small problem in the calculation below. Following is my explaination:

m+x/n+x > m/n =

m+x/n+x - m/n > 0 =

[n(m+x) - m(n+x)]/n(n+x) > 0

[n(m+x) - m(n+x)] > 0

mn + nx - mn - mx > 0

x(n-m) > 0

=> x > 0 & n>m OR x< 0 & n<m

However both of these does not match with the given statements hence the answer should be E.
Senior Manager
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 [#permalink] New post 02 Mar 2007, 10:38
I agree answer has to be C.

I did it this way.

We know that a/b = c/d
then

(a-b)/b = (c-d)/d

If you apply that
Question becomes
Is (m+x-n-x)/(n+x) > (m-n)/n

so

Is (m-n)/(n+x) > (m-n)/n

Stmt 1
m > n ...so numerators are positive...but X is not known to be -ve or +ve...

so NOT SUFF

Stmt 2
x >0..so Denominator on left is greater than that on right...
but Is m-n negative or positive? Not known so we can NOT tell if left > right ( example here is 2 < 5 but -2 > -5... so we need to know the sign)

so NOT SUFF.

If you combine 1 and 2...its SUFF so answer C.
Senior Manager
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 [#permalink] New post 02 Mar 2007, 10:59
grepro
you had it all correct except your last reasoning.

you simplified it to

Is x(n-m) > 0 ?

You can answer this question when you know
Sign of X and Sign of (n-m)

Stmt 1 and 2 combined give you that information. So answer is C.
  [#permalink] 02 Mar 2007, 10:59
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There was a prob with my calc the first time around. I've

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