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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 ## Three machines, A, B, and C, can complete a certain task tagged by: VJesus12 ##### This topic has 1 expert reply and 0 member replies ## Three machines, A, B, and C, can complete a certain task Three machines, A, B, and C, can complete a certain task in 10 hours, 4 hours, and 5 hours respectively. If all 3 machines worked together for 1 hour and then stop, how many hours does it take machine C to complete the job? A. 4/5 B. 9/4 C. 11/4 D. 4 E. 13/2 The OA is B. What is the equation that helps me to solve this DS question? I need your help experts. Thanks. ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 14929 messages Followed by: 1855 members Upvotes: 13060 GMAT Score: 790 Top Reply VJesus12 wrote: Three machines, A, B, and C, can complete a certain task in 10 hours, 4 hours, and 5 hours respectively. If all 3 machines worked together for 1 hour and then stop, how many hours does it take machine C to complete the job? A. 4/5 B. 9/4 C. 11/4 D. 4 E. 13/2 Let the task = the LCM of 10, 4 and 5 = 20 units. Since A takes 10 hours to complete the 20-unit task, A's rate = w/t = 20/10 = 2 units per hour. Since B takes 4 hours to complete the 20-unit task, B's rate = w/t = 20/4 = 5 units per hour. Since C takes 5 hours to complete the 20-unit task, C's rate = w/t = 20/5 = 4 units per hour. Since the combined rate for A+B+C = 2+5+4 = 11 units per hour, the amount of work produced by the 3 machines in 1 hour = 11 units. Since C's rate = 4 units per hour, the time for C to produce the remaining 9 units = w/r = 9/4 hours. The correct answer is B. _________________ Mitch Hunt Private Tutor for the GMAT and GRE GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Student Review #1 Student Review #2 Student Review #3 Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. • FREE GMAT Exam Know how you'd score today for$0

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