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# Which of the following is the closest value of x such that

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 8992
GMAT 1: 760 Q51 V42
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Which of the following is the closest value of x such that  [#permalink]

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07 Jun 2017, 00:23
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55% (hard)

Question Stats:

60% (02:04) correct 40% (02:13) wrong based on 191 sessions

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Which of the following is the closest value of x such that $$x^{20}+x^2+0.0000019=0.09$$?

A. 0.1
B. 0.01
C. 0.3
D. 0.03
E. 0.003

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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" ##### Most Helpful Expert Reply GMAT Club Legend Joined: 11 Sep 2015 Posts: 4875 Location: Canada GMAT 1: 770 Q49 V46 Which of the following is the closest value of x such that [#permalink] ### Show Tags 07 Jun 2017, 07:12 4 Top Contributor 3 MathRevolution wrote: Which of the following is the closest value of x such that $$x^{20}+x^2+0.0000019=0.09$$? A. 0.1 B. 0.01 C. 0.3 D. 0.03 E. 0.003 When a GMAT question tells us to find the "closest value" or the "approximate value," this usually gives us the go ahead to estimate. First recognize that, for all 5 answer choices, the value of x^20 becomes inconsequential For example, if x = 0.1, then x^20 = (0.1)^20 = (1/10)^20 = 1/100000000000000000000 The same applies to all 5 answer choices. Since the value of x^20 has almost no effect on the equation, we can safely ignore it. Likewise, the value 0.0000019 is very very very small in relation to 0.09 So, we can safely ignore it. So, our equation becomes x² ≈ 0.09 Solve to get: x ≈ 0.3 Answer: Cheers, Brent _________________ Test confidently with gmatprepnow.com ##### Most Helpful Community Reply Senior Manager Joined: 28 May 2017 Posts: 276 Concentration: Finance, General Management Re: Which of the following is the closest value of x such that [#permalink] ### Show Tags 07 Jun 2017, 00:36 4 2 MathRevolution wrote: Which of the following is the closest value of x such that $$x^{20}+x^2+0.0000019=0.09$$? A. 0.1 B. 0.01 C. 0.3 D. 0.03 E. 0.003 $$x^{20}+x^2+0.0000019=0.09$$ Nice Question Rather than testing options, one of the best way to solve the solve is to reduce the variables $$x^{20}+x^2+0.0000019=0.09$$ Reduced to $$x^2+0.0000019=0.09$$ Reduced to $$x^2=0.09$$ Voila, x = 0.3 Answer C ##### General Discussion Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 8992 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Which of the following is the closest value of x such that [#permalink] ### Show Tags 09 Jun 2017, 01:35 ==> From $$x^{20}+x^2+0.0000019=0.09, x^{20}$$ and 0.0000019 are very close to 0, so you can ignore them, and the equation becomes $$x^2=0.09=0.3^2$$. Thus, you get x=0.3. 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: Which of the following is the closest value of x such that  [#permalink]

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09 Jun 2017, 07:41
Imo C we can do this question by approximations
Ignore x^20 and 0.0000019
Thus we have
X^2 =0.09

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Re: Which of the following is the closest value of x such that  [#permalink]

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10 Mar 2019, 09:55
This question can be solved by looking at the answer choices and applying logic. Since every time we square a decimal we reduce it's value (i.e. the number of 0s between the decimal point and the number increases), the closest answer would be the the one that has the closest number after being squared, which is C.
Re: Which of the following is the closest value of x such that   [#permalink] 10 Mar 2019, 09:55