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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 ## The surface of a cylinder of radius r and height h... tagged by: swerve ##### This topic has 2 expert replies and 0 member replies ### Top Member ## The surface of a cylinder of radius r and height h... The surface of a cylinder of radius r and height h is painted. The two bases of the cylinder are painted red, and the side of the cylinder is painted green. if the red area is equal to the green area, which of the following must be true? A. h = r B. h = Ï€Â·r C. h = 2r D. h = r/2 E. h = r^2 The OA is A Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks. ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Top Reply Quote: The surface of a cylinder of radius r and height h is painted. The two bases of the cylinder are painted red, and the side of the cylinder is painted green. if the red area is equal to the green area, which of the following must be true? A. h = r B. h = Ï€Â·r C. h = 2r D. h = r/2 E. h = r^2 The OA is A Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. I need your help. Thanks. Hi swerve, Let's take a look at your question. The red area is the area of two circular bases of the cylinder. $$\text{Red Area}=2\pi r^2$$ The green area if equal to the curved surface of the cylinder, i.e. $$\text{Green Area}=2\pi rh$$ If the red area is equal to the green area the, $$2\pi rh=2\pi r^2$$ $$rh=r^2$$ $$h=r$$ 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 swerve, We're told that the surface of a cylinder of radius R and height H is painted: the two bases of the cylinder are painted red, and the side of the cylinder is painted green and the red area is equal to the green area. We're asked which of the following must be true. To answer this question, you first need the area formulas involved. The 'top' and 'bottom' of the cylinder are circles, so each of those two areas is (pi)(R^2). The total of those 2 areas is: (2)(pi)(R^2). The 'side' of the cylinder is the CIRCUMFERENCE of the circle multiplied by the height. That area is (2)(pi)(R)(H). We're told that the two areas are EQUAL to one another, so.... (2)(pi)(R^2) = (2)(pi)(R)(H) You can 'cancel out' the 2s and the pis.... (R^2) = (R)(H) R = H Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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