approach to inequality qs...?

[tj123]

If x-y > 10, is x-y> x+y?

1) x=8
2) y= -20

My approach was this.
If x-y >10, then is x+y< 11?

1) tells me nothing about y, so insuff
2) tells me nothing about x, so insuff

Together they are suff.
I chose C, however this is the wrong answer.

Can someone explain why my thought process on this was wrong?
What is the right way to approach these type of Qs
I will post the OA after some discussion.
thanks.[/spoiler]

[mehravikas]

Statement 1 -> x-8 is it complete?

also is the answer B?

If x-y > 10, is x-y> x+y?

1) x-8
2) y= -20

My approach was this.
If x-y >10, then is x+y< 11?

1) tells me nothing about y, so insuff
2) tells me nothing about x, so insuff

Together they are suff.
I chose C, however this is the wrong answer.

Can someone explain why my thought process on this was wrong?
What is the right way to approach these type of Qs
I will post the OA after some discussion.
thanks.[/spoiler]

[tj123]

x = 8 not x-8

the answer is not b

[manish.sinha]

If x-y > 10, is x-y> x+y?

1) x=8
2) y= -20


Ans: D

I find both the options are able to solove the problem. Taking the statements one by one.

1) When x =8,
for this we have y < -2
for any value of y < -2 we can solve the inequility that x-y > x +y

2) when y = -20 for this we have x>-10
Again for any value for x > -10 we can the inequility solved.

[tj123]

OA is D

[vittalgmat]

If x-y > 10, is x-y> x+y?

1) x=8
2) y= -20

My approach was this.
If x-y >10, then is x+y< 11?

1) tells me nothing about y, so insuff
2) tells me nothing about x, so insuff

Together they are suff.
I chose C, however this is the wrong answer.

Can someone explain why my thought process on this was wrong?
What is the right way to approach these type of Qs
I will post the OA after some discussion.
thanks.[/spoiler]

Here is my approach.

We know that x - y >10 ---(1)
we have to find out if x -y > x +y
Simplyfying the problem
x -y -x -y > 0 ?
-2y > 0?
or we need to find out if y > 0 ?
True or False DS problem.

now consider stmt 1
x =8
plugging x = 8 in x -y > 10 we get a definite answer..
no need to calculate this answer. Just realize we get a definite answer.
And this is enough to answer the True/False DS question.
So Sufficient.

Similarly Stmt 2 is sufficient.

So D.