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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 ## A wheel of a car of radius 21 cms... tagged by: BTGmoderatorLU ##### This topic has 1 expert reply and 0 member replies ### Top Member ## A wheel of a car of radius 21 cms... A wheel of a car of radius 21 cms is rotating at 600 rotations per minute. What is the speed of the car in km/hr? A. 79.2 km/hr B. 47.52 km/hr C. 39.6 km/hr D. 7.92 km/hr E. 3.96 km/hr The OA is B. Can any expert help me with this PS question please? I don't understand it. ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Quote: A wheel of a car of radius 21 cms is rotating at 600 rotations per minute. What is the speed of the car in km/hr? A. 79.2 km/hr B. 47.52 km/hr C. 39.6 km/hr D. 7.92 km/hr E. 3.96 km/hr The OA is B. Can any expert help me with this PS question please? I don't understand it. Hi LUANDATO, Let's take a look at your question. We can see that the radius of the wheel is given in cm. We will first convert it to km because we need to find the speed of the car in km/h. Therefore, Radius = 21 cm = 21/100 m = 0.21m Now convert m to km by dividing 0.21 by 1000, Radius = 0.21/1000 = 0.00021 km We will now find the circumference of the wheel to find out how much distance the wheel will cover in one rotation. $$Circumference=2\pi r$$ $$Circumference=2\times\frac{22}{7}\times0.00021$$ $$Circumference=0.00132\ km$$ So One rotation = 0.00132 km In one minute the wheel is taking 600 rotations per minute. The distance covered in 600 rotations = 600 x Distance covered in one rotation $$=0.00132\ \times600\$$ $$=0.792\ km$$ In one minute the distance covered = 0.792 km In 60 minutes the distance covered = 0.792 x 60 = 47.52 km It means the speed of the car is 47.52 km per hour. Therefore, Option B 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. • FREE GMAT Exam Know how you'd score today for$0

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