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# If x-2y=4, then x^2-4xy+4y^2-x+2y=?

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Math Revolution GMAT Instructor
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If x-2y=4, then x^2-4xy+4y^2-x+2y=?  [#permalink]

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21 Jan 2019, 00:22
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88% (01:04) correct 12% (01:28) wrong based on 41 sessions

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[Math Revolution GMAT math practice question]

If $$x-2y=4$$, then $$x^2-4xy+4y^2-x+2y=$$?

$$A. 12$$
$$B. 16$$
$$C. 20$$
$$D. 24$$
$$E. 28$$

_________________

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 $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Director Joined: 18 Jul 2018 Posts: 679 Location: India Concentration: Finance, Marketing WE: Engineering (Energy and Utilities) Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 21 Jan 2019, 00:25 $$(x-2y)^2 = x^2-4xy+4y^2$$ = 16 $$x^2−4xy+4y^2−x+2y$$ = 16-4 = 12 A is the answer. _________________ Press +1 Kudo If my post helps! Senior Manager Joined: 04 Aug 2010 Posts: 357 Schools: Dartmouth College Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 21 Jan 2019, 03:36 MathRevolution wrote: [Math Revolution GMAT math practice question] If $$x-2y=4$$, then $$x^2-4xy+4y^2-x+2y=$$? $$A. 12$$ $$B. 16$$ $$C. 20$$ $$D. 24$$ $$E. 28$$ Let $$x=4$$ and $$y=0$$, with the result that $$x-2y=4$$. Plugging $$x=4$$ and $$y=0$$ into $$x^2-4xy+4y^2-x+2y=$$, we get: $$4^2-0+0-4+0=12$$ _________________ GMAT and GRE Tutor Over 1800 followers Click here to learn more GMATGuruNY@gmail.com New York, NY If you find one of my posts helpful, please take a moment to click on the "Kudos" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. GMATH Teacher Status: GMATH founder Joined: 12 Oct 2010 Posts: 772 Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 21 Jan 2019, 04:38 MathRevolution wrote: [Math Revolution GMAT math practice question] If $$x-2y=4$$, then $$x^2-4xy+4y^2-x+2y=$$? $$A. 12$$ $$B. 16$$ $$C. 20$$ $$D. 24$$ $$E. 28$$ $$x - 2y = 4\,\,\,\,\,\left( * \right)$$ $$? = \underbrace {{x^2} - 4xy + 4{y^2}}_{{{\left( {x - 2y} \right)}^2}} - x + 2y$$ $$? = {\left( {x - 2y} \right)^2} - \left( {x - 2y} \right)\,\,\,\mathop = \limits_{{\rm{twice}}}^{\left( * \right)} \,\,\,16 - 4 = 12$$ We follow the notations and rationale taught in the GMATH method. Regards, Fabio. _________________ Fabio Skilnik :: GMATH method creator (Math for the GMAT) Our high-level "quant" preparation starts here: https://gmath.net CEO Joined: 11 Sep 2015 Posts: 3447 Location: Canada Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 21 Jan 2019, 06:56 Top Contributor MathRevolution wrote: [Math Revolution GMAT math practice question] If $$x-2y=4$$, then $$x^2-4xy+4y^2-x+2y=$$? $$A. 12$$ $$B. 16$$ $$C. 20$$ $$D. 24$$ $$E. 28$$ GIVEN: x - 2y = 4 We want to find the value of x² - 4xy + 4y² - x + 2y We should notice that x² - 4xy + 4y² is equal to (x - 2y)² We should notice that - x + 2y is equal to -(x - 2y) We get: x² - 4xy + 4y² - x + 2y = (x - 2y)² - (x - 2y) Now replace x - 2y with 4 to get: = (x - 2y)² - (x - 2y) = = (4)² - (4) = 16 - 4 = 12 Answer: A Cheers, Brent _________________ Test confidently with gmatprepnow.com VP Joined: 09 Mar 2018 Posts: 1002 Location: India Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 21 Jan 2019, 07:06 MathRevolution wrote: [Math Revolution GMAT math practice question] If $$x-2y=4$$, then $$x^2-4xy+4y^2-x+2y=$$? $$A. 12$$ $$B. 16$$ $$C. 20$$ $$D. 24$$ $$E. 28$$ IMO A $$x^2-4xy+4y^2-x+2y$$ $$x^2-4xy+4y^2-(x-2y)$$ (a) x-2y = 4 squaring both sides $$x^2-4xy+4y^2=16$$ substituting above in (a) 16 - 4 12 _________________ If you notice any discrepancy in my reasoning, please let me know. Lets improve together. Quote which i can relate to. Many of life's failures happen with people who do not realize how close they were to success when they gave up. Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6985 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=? [#permalink] ### Show Tags 23 Jan 2019, 00:09 => $$x^2-4xy+4y^2-x+2y$$ $$=(x-2y)^2 – (x-2y)$$ $$=4^2 – 4 = 16 – 4 = 12.$$ Therefore, the answer is A. Answer: A _________________ 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$149 for 3 month Online Course"
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Re: If x-2y=4, then x^2-4xy+4y^2-x+2y=?   [#permalink] 23 Jan 2019, 00:09
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# If x-2y=4, then x^2-4xy+4y^2-x+2y=?

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