gmat prep question

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Source: — Data Sufficiency |

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by Neo2000 » Sun May 13, 2007 12:45 am
Only statement 2 suffices.

Statement 1 does not suffice since we do not know the values of m and n

i.e. m & n can be either positive e.g. 8 and 4
or negative -8 and -4

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by jamesk486 » Sun May 13, 2007 2:47 am
could you explain condition 2 pls?

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by jayhawk2001 » Sun May 13, 2007 7:53 am
Neo2000 wrote:Only statement 2 suffices.

Statement 1 does not suffice since we do not know the values of m and n

i.e. m & n can be either positive e.g. 8 and 4
or negative -8 and -4
I don't think 2 suffices as well.

Take m=4, n=2. (2) satisfies condition (4-2)/2 > (4-2)/4 and m > n

Take m=-4, n=-2. (2) satisfies condition (-4+2)/-2 > (-4+2)/-4 but m < n

So, I think it should be E

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by atarafder » Sun May 13, 2007 10:07 am
(m-n)/n > (m-n)/m

multiply both sides by mn/(m-n)

you get m> n, so I think 2 should suffice.

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by atarafder » Sun May 13, 2007 10:11 am
actually I realized I can do the same approach with 1 too -
m/n >1

multiply both sides by n and you get m>n

So should we test with some random values instead of this approach? Any ideas?

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by jayhawk2001 » Sun May 13, 2007 11:40 am
atarafder wrote:(m-n)/n > (m-n)/m

multiply both sides by mn/(m-n)

you get m> n, so I think 2 should suffice.
You can multiply both sides by mn/(m-n) but you don't know what to do
with the inequality sign -- does it reverse in direction or does it remain
the same ?

Put another way

(m-n)/n > (m-n)/m

If m-n is positive, you can do

1/n > 1/m

else, it becomes

1/n < 1/m