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There was a prob with my calc the first time around. I've [#permalink]
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02 Mar 2007, 00:14
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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, 04:40, edited 5 times in total.



Manager
Joined: 12 May 2006
Posts: 179

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(nm) > 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
Joined: 29 Jan 2007
Posts: 441
Location: Earth

I agree answer has to be C.
I did it this way.
We know that a/b = c/d
then
(ab)/b = (cd)/d
If you apply that
Question becomes
Is (m+xnx)/(n+x) > (mn)/n
so
Is (mn)/(n+x) > (mn)/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 mn 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
Joined: 29 Jan 2007
Posts: 441
Location: Earth

grepro
you had it all correct except your last reasoning.
you simplified it to
Is x(nm) > 0 ?
You can answer this question when you know
Sign of X and Sign of (nm)
Stmt 1 and 2 combined give you that information. So answer is C.










