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• The winning strategy for 700+ on the GMAT

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M60-13

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6625
GMAT 1: 760 Q51 V42
GPA: 3.82

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11 Jun 2018, 05:16
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Question Stats:

50% (00:43) correct 50% (00:10) wrong based on 8 sessions

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Is $$x|y|=xz?$$

1) $$x$$, $$y$$, and $$z$$ are positive

2) $$y^2=z^2$$

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6625 GMAT 1: 760 Q51 V42 GPA: 3.82 Re M60-13 [#permalink] Show Tags 11 Jun 2018, 05:16 Official Solution: Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question. Modifying the question: $$x|y| = xz$$ ⇔ $$x(|y|-z) = 0$$ ⇔ $$x = 0$$ or $$|y| = z$$ ⇔ $$x = 0$$ or $$y = z$$ or $$y = -z$$ Since we have 3 variables ($$x$$, $$y$$, and $$z$$) and 0 equations, E is most likely to be the answer. So, we should consider conditions 1) & 2) together first. Conditions 1) & 2): Condition 2) tells us that $$y = z$$ or $$y = -z$$. Since condition 1) states that $$x, y, z > 0$$, we can only have $$y = z$$. Thus, both conditions are sufficient, when taken together. Therefore, the answer is C. In cases where 3 or more additional equations are required, such as for original conditions with "3 variables", or "4 variables and 1 equation", or "5 variables and 2 equations", conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2), when taken together. Obviously, there may be occasions on which the answer is A, B, C or D. Answer: C _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
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Intern
Joined: 23 Oct 2015
Posts: 16
Location: Bahrain

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02 Aug 2018, 07:11
Condition 2) tells us that y=z or y=−z

In both the above possibilities, we can sufficiently answer that x |y| = xz ; because the modulus on y will ensure that both z and -z gives out a positive figure.

Why is it that we need the first condition?
Intern
Joined: 18 May 2017
Posts: 2

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13 Aug 2018, 02:30
ShivaniD wrote:
Condition 2) tells us that y=z or y=−z

In both the above possibilities, we can sufficiently answer that x |y| = xz ; because the modulus on y will ensure that both z and -z gives out a positive figure.

Why is it that we need the first condition?

I agree with you. I believe the answer they provided is wrong. This is not the first time REVOLUTION posted a wrong answer.
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Joined: 04 Aug 2018
Posts: 6

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09 Sep 2018, 12:56
1
XIYI =XZ?

Break Down:- IYI = Z (canceling out x)
i.e. Z must be positive. (as IYI is always positive)
So one need to verify that Z is +ve as well as it is equal to Y in magnitude

1) The statement says that Z is +ve . But doesn't tell about magnitude of Z.
Hence Insufficient.

2)The statement says that Z can be + ve OR -ve . But magnitude of Z will be equal to that of Y.
Hence Insufficient.

Combining 1 & 2 , both conditions are satisfied. (Z is +ve as well as it is equal to Y in magnitude)
Re: M60-13 &nbs [#permalink] 09 Sep 2018, 12:56
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