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# If x=0.2, then what is the value of x^3-1/x-1?

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If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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12 Feb 2019, 01:08
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25% (medium)

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77% (01:50) correct 23% (01:34) wrong based on 53 sessions

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[GMAT math practice question]

If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$?

$$A. 1.2$$
$$B. 1.22$$
$$C. 1.24$$
$$D. 1.44$$
$$E. 2.22$$

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"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" NUS School Moderator Joined: 18 Jul 2018 Posts: 1024 Location: India Concentration: Finance, Marketing WE: Engineering (Energy and Utilities) If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags 12 Feb 2019, 01:12 0.2 = 2/10. $$x^3$$ = $$\frac{8}{1000}$$ $$x^3-1$$ = $$\frac{-992}{1000}$$ $$x-1 = \frac{-8}{10}$$ $$\frac{(x^3-1)}{(x-1)}$$ = $$\frac{992}{1000}*\frac{10}{8}$$ = 124/100 = 1.24 C is the answer. _________________ Press +1 Kudos If my post helps! VP Joined: 31 Oct 2013 Posts: 1471 Concentration: Accounting, Finance GPA: 3.68 WE: Analyst (Accounting) Re: If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags 12 Feb 2019, 01:17 MathRevolution wrote: [GMAT math practice question] If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$? $$A. 1.2$$ $$B. 1.22$$ $$C. 1.24$$ $$D. 1.44$$ $$E. 2.22$$ x = 0.02 Given , $$\frac{x^3-1}{x-1}$$ = $$0.2^3$$- 1 / 0.2 - 1 = 0.008 - 1 / - 0.8 = - 0.992 / - 0.8 = 1.24. The best answer is C. e-GMAT Representative Joined: 04 Jan 2015 Posts: 3074 If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags Updated on: 13 Feb 2019, 22:34 Solution Given: • The value of x = 0.2 To find: • The value of the expression $$\frac{x^3 – 1}{x – 1}$$ Approach and Working: We know that • $$x^3 – 1 = (x – 1) (x^2 + x + 1)$$ Therefore, $$\frac{x^3 – 1}{x – 1} = x^2 + x + 1$$ Now, if x = 0.2 • The value of the given expression = $$(0.2)^2 + 0.2 + 1 = 0.04 + 0.2 + 1 = 1.24$$ Hence, the correct answer is option C. Answer: C _________________ Originally posted by EgmatQuantExpert on 12 Feb 2019, 02:36. Last edited by EgmatQuantExpert on 13 Feb 2019, 22:34, edited 1 time in total. Target Test Prep Representative Status: Founder & CEO Affiliations: Target Test Prep Joined: 14 Oct 2015 Posts: 8048 Location: United States (CA) Re: If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags 12 Feb 2019, 21:09 MathRevolution wrote: [GMAT math practice question] If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$? $$A. 1.2$$ $$B. 1.22$$ $$C. 1.24$$ $$D. 1.44$$ $$E. 2.22$$ ((0.2)^3 - 1)/(0.2 - 1) (0.008 - 1)/(-0.8) (-0.992)/(-0.8) = 1.24 Alternate solution: The formula for factoring the difference of cubes is (x^3 - 1) = (x - 1)(x^2 + x +1). We can use that fact to simplify (x^3 - 1)/(x - 1) = x^2 + x + 1. Therefore, when x = 0.2, we have: (0.2)^2 + 0.2 + 1 = 0.04 + 0.2 + 1 = 1.24 Answer: C _________________ # Scott Woodbury-Stewart Founder and CEO Scott@TargetTestPrep.com 122 Reviews 5-star rated online GMAT quant self study course See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews If you find one of my posts helpful, please take a moment to click on the "Kudos" button. Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 8007 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags 14 Feb 2019, 02:02 => $$\frac{x^3-1}{x-1} = \frac{(x-1)(x^2+x+1)}{x-1}= x^2+x+1$$ Plugging in $$x = 0.2$$ yields $$x^2+x+1 = (0.2)^2 + (0.2) + 1 = 0.04 + 0.2 + 1 = 1.24$$ Therefore, the answer is C. 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$79 for 1 month Online Course"
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Re: If x=0.2, then what is the value of x^3-1/x-1?   [#permalink] 14 Feb 2019, 02:02
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