theCodeToGMAT wrote:rakeshd347 wrote:
Let me ask you one thing.
In your solution in this question what have you done:
x - y + 1 > x + y - 1
=> -2y > -2 (You subtracted X from both sides and subtracted Y on both sides)
=> y < 1 ??
What you have recommended above to Sri you have done yourself. Now you might argue that you have not subtracted or added but you have cancelled out X. that is one and same thing cancelling out or subtracting is same thing.
Rakesh, you cannot simply add variables on the inequalities by adding both the variable on both sides are replacing 0 by "x - x"
THe GMAT Instructor has also clearly stated that it's always a big risk involved when you are trying to do that. Also, the outcome is that my Answer turned out to be "D" rather than "B". It's correct to add definite numeric number but playing with Variables can be very risky.
The point which you are raising is a simple mathematic concept; if you apply the same method in inequality then your are going to get many incorrect inequalities answers simply because you can introduce any variable from anywhere you want and prove the inequality as per the desired motive. Also, I dint introduce any new variable in my solution; I have simply eliminated and elimination is very different from addition of new variables. If you apply a similar approach then I can give you many such question wherein you can get Answers as {A} but infact the OA won;t be {A}
The question put up by "Sri" is very clear.. he wants to know whether we can play with variables ..
Here is the question asked by Sri:
My approach:
Is, x - y + 1 > x + y - 1
i.e. -y + 1 > y - 1
I was wondering if it is correct here to add y on both sides?
i.e. -y + 1 + y > y - 1 + y
i.e. 1 > 2y - 1
I was not sure if this is correct since we don't know whether y is positive or negative. Can you please clarify? Thanks a lot.
Best Regards,
Sri
He is not doing x-x=0
Now in here can you show me what new variable he has introduced. All he has asked is that is it alright to do this:
-y+1>y-1 ( he is asking is it alright to add Y on both sides and my answer is yes it is absolutely alright to add Y on both side but you said its not)
Now if he add Y on both sides he gets
1>2y-1 or 2>2y or 1>y or Y<1
This is what you calculated in your answer explanation. In your other question what you have done is wrong. But to Sri's answer it is absolutely fine to add the same variable on both sides of the inequality.
If you don't agree with me can you justify your answer in this question. I think you are mixing two different things here. I am directing to Sri's question is that you can add or subtract the same variable from both sides and that is what you have done in your solution.
Thanks,
Rakesh
