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If 3x + y = − 1 and y − 2x = 4, what is the value of x + 2y?

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Carcass
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If 3x + y = − 1 and y − 2x = 4, what is the value of x + 2y? [#permalink] New post   02 Mar 2019, 11:27
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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
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MagooshStudentHelp
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Re: If 3x + y = − 1 and y − 2x = 4, what is the value of x + 2y? [#permalink] New post   10 Mar 2019, 10:41
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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!
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Re: If 3x + y = 1 and y 2x = 4, what is the value of x + 2y? [#permalink] New post   23 Mar 2022, 11:55
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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

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
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Re: If 3x + y = 1 and y 2x = 4, what is the value of x + 2y? [#permalink] New post   28 Apr 2024, 16:54
Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If 3x + y = 1 and y 2x = 4, what is the value of x + 2y? [#permalink]
28 Apr 2024, 16:54
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