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Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
If 6x - 15y = 33, and 6y - x = -18, what is the
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04 Aug 2020, 09:15
04 Aug 2020, 09:15
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Question Stats:
86% (01:50) correct
13% (04:52) wrong based on 22 sessions
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If 6x - 15y = 33, and 6y - x = -18, what is the sum of x and y?
(A) -7
(B) -5
(C) 2
(D) 5
(E) 12
Note: This post is part of my Pro Tip series. You'll find my analysis and full solution below.
(A) -7
(B) -5
(C) 2
(D) 5
(E) 12
Note: This post is part of my Pro Tip series. You'll find my analysis and full solution below.
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: If 6x - 15y = 33, and 6y - x = -18, what is the
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05 Aug 2020, 05:56
05 Aug 2020, 05:56
1
GreenlightTestPrep wrote:
If 6x - 15y = 33, and 6y - x = -18, what is the sum of x and y?
(A) -7
(B) -5
(C) 2
(D) 5
(E) 12
Note: This post is part of my Pro Tip series. You'll find my analysis and full solution below.
We're given the following system of equations: (A) -7
(B) -5
(C) 2
(D) 5
(E) 12
Note: This post is part of my Pro Tip series. You'll find my analysis and full solution below.
6x - 15y = 33
6y - x = -18
OBSERVATION #1: In the top equation, all three terms (6x, 15y and 33) are divisible by 3.
So, we can create a simpler, yet equivalent, equation by dividing both sides by 3 to get:
2x - 5y = 11
6y - x = -18
OBSERVATION #2: The x and y terms of the two equations are arranged differently.
So let's rewrite the bottom equation as follows:
2x - 5y = 11
-x + 6y = -18
OBSERVATION #3: The question is NOT asking us to determine the individual values of x and y; it's asking us to find the SUM of x and y (i.e., x + y)
Important: When it comes to solving systems of equations like this, there are two possible approaches:
i) The substitution method, where you solve one equation for a particular variable, and then substitute that into the other equation and solve.
ii) The elimination method, where you can either add or subtract equations to eliminate a variable.
In most cases, the elimination method is faster, so be sure to know it.
Notice that, if we take the following system...
2x - 5y = 11
-x + 6y = -18
... and ADD the two equations we get: x + y = -7
Answer: A
If you're up for it, here's another question involving a system of equations: https://gre.myprepclub.com/forum/topic19312.html
Cheers,
Brent
Re: If 6x - 15y = 33, and 6y - x = -18, what is the
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14 Feb 2024, 12:52
14 Feb 2024, 12:52
Hello from the GRE Prep Club BumpBot!
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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).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
