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by gmatfailed » Wed Jun 16, 2010 4:17 am
. - DS
are x and y both positive?
(1) 2x - 2y = 1
(2) x/y > 1

Why is the answer C?


when we combine 1 and 2

X could be 0 when y is -1/2

so X is non-negative and non-positive whereas Y is negative

therefore we could have x and y both positive as well as X as 0 and y negative, and still satisfy the X>y and x-y=1/2
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by kvcpk » Wed Jun 16, 2010 4:26 am
Are you sure that the OA is c?
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by amising6 » Wed Jun 16, 2010 4:35 am
from stament 1)2x-2y=1 dividing both side by 2
we have x-y=1/2
so this is not sufficient

from 2)x/y>1
so we can say x>y

from 1&2 we can say x and y are positive as xis greater than y and there difference is positive
to cross check you can plug some numbers and c for yourself
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by gmatfailed » Wed Jun 16, 2010 5:35 am
Buddy,

do you agree 0 is greater than -1/2?

so if x = 0 and y = -1/2

x-y= 1/2


so here o is non negative or non positive whereas y is negative
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by amising6 » Wed Jun 16, 2010 5:42 am
yes c 0 is neither positive nor negative so its definately gretaet than -1/2
because on numberline o lies on the right hand side of any negative number
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by gmatfailed » Wed Jun 16, 2010 5:53 am
The question states are x and y positive?
The answer is both no and yes.
therefore the solution should be E
We can have 0 for x and -1/2 for y. Also x could be 1 and y = 1/2. In both cases X is greater than y but x is not necessarily positive.
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by amising6 » Wed Jun 16, 2010 6:00 am
yes it seems logical
i misread the question
answer should be E
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by rackbar » Wed Jun 16, 2010 6:07 am
If x = 0, and y = -1/2 then x/y is not greater than one. Zero divided by anything is still zero. You took the second constraint to mean that x is greater than y, but this is not necessarily true.

What if both x and y are negative?
Such as, x = -15, y =-10. Then x would be less than y, but x/y would still be greater than 1.
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by kvcpk » Wed Jun 16, 2010 7:36 am
kvcpk wrote:Are you sure that the OA is c?
I dont know how I missed it.. Answer is C.
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