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Source: — Data Sufficiency |
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by cans » Tue May 31, 2011 8:08 pm
to find if both x,y>0
a) 2x-2y=0 or 2x=2y or x=y
it means they can both be negative, or positive or zero.
insufficient.
b) x/y>0
if x=1, y =2; 1/2>0 true
if x=-1,y=-2; -1/-2=1/2>0 true
hence we can't say they both are positive. Insufficient.
Both A & B together: x=y and x/y = y/y = 1 which is always greater than 0,
Thus insufficient.
IMO E
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by SoCan » Tue May 31, 2011 8:30 pm
As cans said, statement 1 just means that x and y are equal, but they could be positive or negative.

For the second statement - a quick way to think about x/y>0 is that the sign of x and y are the same. You don't have to spend time plugging in numbers - just ask yourself if knowing that both signs are the same is sufficient to answer the question.
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by Spartacus2000 » Thu Jun 02, 2011 5:58 am
My mistake.

The first statement is 2x - 2y = 1.

Sorry about that.
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by cans » Thu Jun 02, 2011 6:27 am
Spartacus2000 wrote:My mistake.

The first statement is 2x - 2y = 1.

Sorry about that.
a)2x-2y=1 => x = y + 1/2
x&y can be of any sign. For ex (x,y): (0,-1/2) (1,1/2) (-1/2,-1) and so on....
Insufficient.

b)x/y>0 => x and y are of same sign. Either both are positive or both are negative
Thus insufficient.

a & b together) x= y + 1/2 and x,y have same sign.
still insufficient as (1,1/2) & (-1/2,-1) both satisfy these conditions.
Thus IMO E
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by pemdas » Thu Jun 02, 2011 8:40 pm
-1=-1/2+1/2 doesn't satisfy the condition 2x-2y=1

from statement (1) x is greater than y, as x=y+1/2 for the positive signs, and x is less than y for the negative signs.
from statement (2) x/y>0 is true for all non-zero y, when x is greater than y for the positive signs, and x is less than y for the negative signs.
combining both statements we get the same conditions, hence no restriction for x and y as being positive.

it must be e
cans wrote:
Spartacus2000 wrote:My mistake.

The first statement is 2x - 2y = 1.

Sorry about that.
a)2x-2y=1 => x = y + 1/2
x&y can be of any sign. For ex (x,y): (0,-1/2) (1,1/2) (-1/2,-1) and so on....
Insufficient.

b)x/y>0 => x and y are of same sign. Either both are positive or both are negative
Thus insufficient.

a & b together) x= y + 1/2 and x,y have same sign.
still insufficient as (1,1/2) & (-1/2,-1) both satisfy these conditions.
Thus IMO E
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by cans » Thu Jun 02, 2011 9:35 pm
pemdas wrote:-1=-1/2+1/2 doesn't satisfy the condition 2x-2y=1

from statement (1) x is greater than y, as x=y+1/2 for the positive signs, and x is less than y for the negative signs.
from statement (2) x/y>0 is true for all non-zero y, when x is greater than y for the positive signs, and x is less than y for the negative signs.
combining both statements we get the same conditions, hence no restriction for x and y as being positive.

it must be e
cans wrote:
Spartacus2000 wrote:My mistake.

The first statement is 2x - 2y = 1.

Sorry about that.
a)2x-2y=1 => x = y + 1/2
x&y can be of any sign. For ex (x,y): (0,-1/2) (1,1/2) (-1/2,-1) and so on....
Insufficient.

b)x/y>0 => x and y are of same sign. Either both are positive or both are negative
Thus insufficient.

a & b together) x= y + 1/2 and x,y have same sign.
still insufficient as (1,1/2) & (-1/2,-1) both satisfy these conditions.
Thus IMO E
I never used(-1,-1/2) as a point. I was other way round (-1/2,-1)
If my post helped you- let me know by pushing the thanks button ;)

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Cans!!
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by pemdas » Thu Jun 02, 2011 10:27 pm
ok, (1,1/2) and (-1/2,-1) are still (x,y)? the values are changing with signs then
that's the reason i posted above
and Yes, with (-1/2;-1) works for both statements, BUT then (1/2;1) doesn't work again

you are changing not only signs but values too in your example, agree?
cans wrote:
pemdas wrote:-1=-1/2+1/2 doesn't satisfy the condition 2x-2y=1

from statement (1) x is greater than y, as x=y+1/2 for the positive signs, and x is less than y for the negative signs.
from statement (2) x/y>0 is true for all non-zero y, when x is greater than y for the positive signs, and x is less than y for the negative signs.
combining both statements we get the same conditions, hence no restriction for x and y as being positive.

it must be e
cans wrote:
Spartacus2000 wrote:My mistake.

The first statement is 2x - 2y = 1.

Sorry about that.
a)2x-2y=1 => x = y + 1/2
x&y can be of any sign. For ex (x,y): (0,-1/2) (1,1/2) (-1/2,-1) and so on....
Insufficient.

b)x/y>0 => x and y are of same sign. Either both are positive or both are negative
Thus insufficient.

a & b together) x= y + 1/2 and x,y have same sign.
still insufficient as (1,1/2) & (-1/2,-1) both satisfy these conditions.
Thus IMO E
I never used(-1,-1/2) as a point. I was other way round (-1/2,-1)
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