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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## If the radius of a cylinder is doubled and so... tagged by: BTGmoderatorLU ##### This topic has 2 expert replies and 0 member replies ### Top Member ## If the radius of a cylinder is doubled and so... If the radius of a cylinder is doubled and so is the height, what is the new volume of the cylinder divided by the old one? A. 8 B. 2 C. 6 D. 4 E. 10 The OA is A. I know that the area of a cylinder is, $$2\pi\cdot r^2\cdot h$$ But, I'm confused with this PS question. Experts, any suggestion? Thanks in advance. ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Top Reply Quote: If the radius of a cylinder is doubled and so is the height, what is the new volume of the cylinder divided by the old one? A. 8 B. 2 C. 6 D. 4 E. 10 The OA is A. I know that the area of a cylinder is, $$2\pi\cdot r^2\cdot h$$ But, I'm confused with this PS question. Experts, any suggestion? Thanks in advance. Hi LUANDATO, Let's take a look at your question. If radius if a cylinder is r and height is h, the volume of the cylinder is: $$V=\pi r^2h$$ If the radius of the cylinder is doubled and so is the height, the volume of the cylinder can be calculated as, $$V_1=\pi\left(2r\right)^2\left(2h\right)$$ $$V_1=\pi\left(4\right)r^2\left(2h\right)$$ $$V_1=8\pi r^2h$$ The new volume of the cylinder divided by the old one will be: $$\frac{V_1}{V}=\frac{8\pi r^2h}{\pi r^2h}$$ $$\frac{V_1}{V}=8$$ Therefore, Option A is correct. Hope it helps. I am available if you'd like any follow up. _________________ GMAT Prep From The Economist We offer 70+ point score improvement money back guarantee. Our average student improves 98 points. Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now. ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 497 members Upvotes: 2867 GMAT Score: 800 Top Reply Hi LUANDATO, We're told that the radius of a cylinder and its height are both DOUBLED. We're asked for the result when the 'new' volume of the cylinder divided by the 'old' one. This question can be solved in a couple of different ways. Here's how you can solve it by TESTing VALUES. Volume of a cylinder = (pi)(R^2)(H) where R is the radius and H is the height. IF.... Old cylinder has R=1 and H=1, then it's Volume = (pi)(1^2)(1) = 1pi New cylinder has R=2 and H=2, so it's Volume = (pi)(2^2)(2) = 8pi The 'new' volume divided by the 'old' volume = 8pi/1pi = 8 Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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