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# X is proportional to Y. If Y is increased by 30%, by approximately

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5280
GMAT 1: 800 Q59 V59
GPA: 3.82
X is proportional to Y. If Y is increased by 30%, by approximately [#permalink]

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13 Mar 2018, 00:56
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Difficulty:

55% (hard)

Question Stats:

53% (01:22) correct 47% (01:34) wrong based on 43 sessions

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[GMAT math practice question]

$$X$$ is proportional to $$Y$$. If $$Y$$ is increased by $$30%$$, by approximately what percent is $$X^2$$ increased?

$$A. 30%$$
$$B. 40%$$
$$C. 50%$$
$$D. 60%$$
$$E. 70%$$
[Reveal] Spoiler: OA

_________________

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 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" PS Forum Moderator Joined: 25 Feb 2013 Posts: 1059 Location: India GPA: 3.82 X is proportional to Y. If Y is increased by 30%, by approximately [#permalink] ### Show Tags 13 Mar 2018, 11:33 MathRevolution wrote: [GMAT math practice question] $$X$$ is proportional to $$Y$$. If $$Y$$ is increased by $$30%$$, by approximately what percent is $$X^2$$ increased? $$A. 30%$$ $$B. 40%$$ $$C. 50%$$ $$D. 60%$$ $$E. 70%$$ $$x$$ is proportional to $$y$$ so let $$x=ky$$, where $$k$$ is constant of proportionality so $$x^2=(ky)^2$$. When $$y$$ is increased by $$30$$%, $$x=1.3ky$$, so $$x^2=1.69(ky)^2$$ Hence there is an increase of $$0.69$$ or $$69$$% in the value of $$x^2$$. Nearest option is $$70$$% Option E Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 5280 GMAT 1: 800 Q59 V59 GPA: 3.82 Re: X is proportional to Y. If Y is increased by 30%, by approximately [#permalink] ### Show Tags 15 Mar 2018, 02:24 => $$X = kY$$ for some $$k$$. Since $$(1.3kY)^2 = 1.69k^2Y^2 = 1.69(kY)^2 = 1.69X^2$$, we have $$\frac{(1.69X^2 – X^2)}{X^2} = 0.69$$, which is approximately 70%. Therefore, the answer is E. Answer: E _________________ 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 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
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Re: X is proportional to Y. If Y is increased by 30%, by approximately   [#permalink] 15 Mar 2018, 02:24
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