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GMAT Prep DS Q.

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Source: — Data Sufficiency |
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by xcusemeplz2009 » Sat Nov 07, 2009 7:27 am
IMO C

statement1) m-3z>0 => m>3z not suff.

s2) 4z-m<0=>m>4z => not suff

again s2) can be written as m-4z>0

now sub 1 and 2
m-3z-m+4z>0
z>0

since m-3z>0 and z>0=>m>0

hence M+Z>0

using bth suff.
Hence C
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Re: GMAT Prep DS Q.

by palvarez » Sat Nov 07, 2009 5:35 pm
italian7745 wrote:Is m + z >0

1) m-3z>0
2) 4z-m<0

1. m > 3z, or m +z > 4z

we need to know whether z is +ve.

2. m > 4z or m + z > 5z.

Same thing, we need to know whether z is +ve

combining together

m > 3z & m > 4z

case1:

m > 3z > 4z, in this case, z is negative. Insufficient, since m + z is greater than a negative number, meaning that m+z can be +ve or -ve.

case 2:

m > 4z > 3z, z is +ve, m +z is +ve.


E is the answer
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by palvarez » Sat Nov 07, 2009 5:39 pm
xcusemeplz2009 wrote:IMO C

statement1) m-3z>0 => m>3z not suff.

s2) 4z-m<0=>m>4z => not suff

again s2) can be written as m-4z>0

now sub 1 and 2
m-3z-m+4z>0
z>0
Subtraction doesn't preserve inequalities.


a > c
b > d

can we prove that a - b > c - d ?

Nope.

a = c + k, k > 0
b = d + l, l > 0

a - b = c - d + (k-l)

a -b > c - d only when k > l, which we don't know.

However, a + b > c + d

since a + b = c + d + (k +l)

k +l > 0, therefore a + b > c + d
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