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approach to inequality qs...?

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approach to inequality qs...?

by tj123 » Sun Jul 12, 2009 3:39 pm
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]
Last edited by tj123 on Sun Jul 12, 2009 5:51 pm, edited 1 time in total.
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Re: approach to inequality qs...?

by mehravikas » Sun Jul 12, 2009 5:25 pm
Statement 1 -> x-8 is it complete?

also is the answer B?
tj123 wrote: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]
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by tj123 » Sun Jul 12, 2009 5:51 pm
x = 8 not x-8

the answer is not b
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by manish.sinha » Sun Jul 12, 2009 7:47 pm
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.
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by tj123 » Sun Jul 12, 2009 9:22 pm
OA is D
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Re: approach to inequality qs...?

by vittalgmat » Sun Jul 12, 2009 9:33 pm
tj123 wrote: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.
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