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by gmatboost » Thu Aug 25, 2011 10:24 pm
This is a classic case for picking numbers on DS inequalities.

1.
x = 3, y = 2 -> 1/5
x = 3, y = -2 -> 5/1

2.
x = 3, y = -2 -> 5/1 (REUSE!)
x = -3, y = -2 -> -1/-5 = 1/5

Combined:
x = 3, y = -2 -> 5/1 (REUSE!)
x = 3, y = -4 -> 7/-1

The keys to this strategy:
Pick positives and negatives
Don't pick 1
Pick numbers that are a little bigger and a little smaller than the other numbers you are picking. Notice my use of 2, 3, 4, -2, -3, -4.
Reuse examples whenever you can.
Keep picking different types of numbers. For example, don't pick 3 and -2, and then pick 3 and -1. Both of those give you x + y > 0. We want to mix things up! That's why I chose 3 and -4.
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by prateek_guy2004 » Fri Aug 26, 2011 8:35 am
jainrahul1985 wrote:If x not equal to -y, is (x-y)/(x+y) > 1 ?
(1) x > 0
(2) y < 0

OA E
Mate dont mention answer..The fun goes if you read answer before reading ques's.
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by force5 » Fri Aug 26, 2011 12:45 pm
gmatboost... is there any strategy for doing such questions. i find picking numbers very less convincing. Its a risk a lot of times.
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by gmatboost » Fri Aug 26, 2011 2:25 pm
Almost any question can be approached both by picking numbers and using algebra. The specific algebra varies by question, so it's tough to generalize.

Here, when you learn that x > 0 and y < 0, you should be able to figure out a few things:
x - y > 0
x + y could be positive, negative or zero
x - y > x + y

The "cases" to consider here are probably
1. x + y > 0
2. x + y = 0
3. x + y < 0

1. (x-y)/(x+y) is > 1
2. Impossible, cannot divide by 0
3. (x-y)/(x+y) is negative

Every question is a little different, but in general you are often trying to determine:
1. What's positive? What's negative? What could be either?
2. Which is greater?
3. Are we talking about a quantity that is > 1, between 0 and 1, between -1 and 0, or < -1.

These same questions should be in your mind when you choose numbers to plug in.

Hope this is at least a little helpful. Don't hesitate to ask follow up questions!
Greg Michnikov, Founder of GMAT Boost

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by bblast » Fri Aug 26, 2011 10:07 pm
Hi Greg,

The answer would be C if we were given another condition from the stem. |x| > |y|.
Correct ?
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by gmatboost » Sun Aug 28, 2011 9:14 am
That's correct.
If |x| > |y|, we would know that x + y > 0.

And since we know that (x-y)>(x+y), we could conclude that
(x-y)/(x+y) > 1
Greg Michnikov, Founder of GMAT Boost

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by navami » Wed Aug 31, 2011 12:46 am
option 2 is not useful at all.

E is the choice.
The key clue should be whether x>Y or x<Y
This time no looking back!!!
Navami
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