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If 3x + y = − 1 and y − 2x = 4, what is the value of x + 2y?
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02 Mar 2019, 11:27
02 Mar 2019, 11:27
Expert Reply
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Question Stats:
70% (00:52) correct
30% (00:22) wrong based on 70 sessions
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If \(3x + y = − 1\) and \(y − 2x = 4\), what is the value of \(x + 2y\)?
A. − 5
B. − 3
C. 0
D. 3
E. 5
A. − 5
B. − 3
C. 0
D. 3
E. 5
Re: If 3x + y = − 1 and y − 2x = 4, what is the value of x + 2y?
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10 Mar 2019, 10:41
10 Mar 2019, 10:41
Expert Reply
We could solve for x and then solve for y and then solve for x + 2y. However, whenever the test asks you to solve for an expression, then there's almost always a neat shortcut you can use to get it.
Here's our two equations:
3x + y = − 1
y − 2x = 4
For clarity, I'll rewrite the top equation slightly:
y + 3x = − 1
y − 2x = 4
And now I'll just add the two equations:
2y + x = 3
And how convenient, that's the answer we were looking for!
Here's our two equations:
3x + y = − 1
y − 2x = 4
For clarity, I'll rewrite the top equation slightly:
y + 3x = − 1
y − 2x = 4
And now I'll just add the two equations:
2y + x = 3
And how convenient, that's the answer we were looking for!
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Re: If 3x + y = 1 and y 2x = 4, what is the value of x + 2y?
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23 Mar 2022, 11:55
23 Mar 2022, 11:55
1
Carcass wrote:
If \(3x + y = − 1\) and \(y − 2x = 4\), what is the value of \(x + 2y\)?
A. − 5
B. − 3
C. 0
D. 3
E. 5
A. − 5
B. − 3
C. 0
D. 3
E. 5
Important: Notice that the question is not asking us to find the individual values of x and y. On the GRE, this often means we can determine the answer without finding the individual values. That's the case here
Given:
3x + y = − 1
y − 2x = 4
Rearrange the bottom equation as follows:
3x + y = − 1
−2x + y = 4
ADD the two equations to get: x + 2y = 3
Answer: D
