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16 Sep 2018, 09:05
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A
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Difficulty:
5%
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Question Stats:
96% (00:53) correct
4%
(01:38)
wrong
based on 51
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If y=3x, what is the value of x+y?
1) 3y=4x+21
2) x<y
Source: GMAT Prep Course, Jeff Kolby
1) 3y=4x+21
2) x<y
Source: GMAT Prep Course, Jeff Kolby
Pure algebraic questions like this one are no longer part of the GMAT Data Sufficiency syllabus.
For relevant Data Sufficiency questions, please check the Data Sufficiency forum:
Data Sufficiency Forum
Data Sufficiency Forum
16 Sep 2018, 10:25
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x+y can also be written as x+3x = 4x
1) 3y=4x+21
Substituting y with 3x in the equation
9x = 4x+21, therefore we can find the value of x and thus 4x or x+y - Sufficient
2) x<y
This does not give us unique values for x and y
if x = 1, then y = 3, and x+y=4
if x = 2, then y = 6, and x+y=8
x+y has no unique value - Insufficient
Answer: A
1) 3y=4x+21
Substituting y with 3x in the equation
9x = 4x+21, therefore we can find the value of x and thus 4x or x+y - Sufficient
2) x<y
This does not give us unique values for x and y
if x = 1, then y = 3, and x+y=4
if x = 2, then y = 6, and x+y=8
x+y has no unique value - Insufficient
Answer: A
17 Sep 2018, 11:18
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bettatantalo
Target question: What is the value of x+y?
Given: y = 3x
Statement 1: 3y = 4x + 21
We also know that y = 3x
Since we have two DIFFERENT linear equations with 2 variables, we COULD solve the system of equations for x and y, which means we COULD determine the value of x+y (Of course, we'd never waste valuable time actually solving the system)
Since we COULD answer the target question with certainty, statement 1 is SUFFICIENT
Statement 2: x < y
There are several values of x and y that satisfy statement 2 (And satisfy the given information). Here are two possible cases:
Case a: x = 1 and y = 3. In this case, the answer to the target question is x + y = 4
Case b: x = 2 and y = 6. In this case, the answer to the target question is x + y = 8
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT
Answer: B
Cheers,
Brent
