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JonDStewart
- Newbie | Next Rank: 10 Posts
- Posts: 5
- Joined: Thu Jul 02, 2009 10:13 pm
using the Kaplan book, the new GMAT Premier Live Online one, and I have this question
30. What is the value of 2x-y
a) x + y = 12
b) X-y = 4
now the way I did it was,
to use (a) x + y = 12
x = 12 -y
plug that into 2x-y to get
2(12-y) -y = 0
24-2y-y = 0
24-3y = 0
-3y= -24
y = 8
plug 8 into x + y = 12 to get x = 4, add those both back into original 'what is the value of 2x-y' to get an answer.
(b) same process
Now the book says that there is no way to get a unique value using this process and that you have to use both A and B to get unique values (I know how to do this, I just thought I could do it quicker the way I did it). So I guess my question is, am I not allowed to do what I did?
When I subtracted 24 from both sides, even though I don't know if other side is zero. Can I not just use zero on the other side? Question is what is 2x-y and I took it as kind of a 2x-y=0 to add the 24...
Like I said, kind of a silly question as I'm guessing I'm just not allowed to do that.
Thanks!
30. What is the value of 2x-y
a) x + y = 12
b) X-y = 4
now the way I did it was,
to use (a) x + y = 12
x = 12 -y
plug that into 2x-y to get
2(12-y) -y = 0
24-2y-y = 0
24-3y = 0
-3y= -24
y = 8
plug 8 into x + y = 12 to get x = 4, add those both back into original 'what is the value of 2x-y' to get an answer.
(b) same process
Now the book says that there is no way to get a unique value using this process and that you have to use both A and B to get unique values (I know how to do this, I just thought I could do it quicker the way I did it). So I guess my question is, am I not allowed to do what I did?
When I subtracted 24 from both sides, even though I don't know if other side is zero. Can I not just use zero on the other side? Question is what is 2x-y and I took it as kind of a 2x-y=0 to add the 24...
Like I said, kind of a silly question as I'm guessing I'm just not allowed to do that.
Thanks!
