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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 operating independently, simultaneously, tagged by: Vincen ##### This topic has 2 expert replies and 0 member replies ### Top Member ## Three machines operating independently, simultaneously, Three machines operating independently, simultaneously, and at the same constant rate can fill a certain production order in 36 hours. If one additional machine were used under the same operating conditions, in how many fewer hours of simultaneous operation could the production order be fulfilled? A. 6 B. 9 C. 12 D. 27 E. 48 The OA is B. I made some calculus and I got 27. Experts, may you show me how to solve this PS question? Thanks. ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Hello Vincen. Let's take a look at your question. 3 machines ------ 36 hours 4 machines ------- x hours Then x=3*36/4 = 27 hours. But the question says "in how many fewer hours..." Now, if 3 machines spend 36 hours and 4 machines spend 27 hours to do the work, then the work could be done in 9 hours less. So, the correct answer is B. I hope this explanation may help you. I'm available if you'd like a follow up. Regards. _________________ 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 Hi Vincen, We're told that 3 machines operating independently, simultaneously, and at the same constant rate can fill a certain production order in 36 hours. We're asked if one additional machine were used under the same operating conditions, in how many FEWER hours of simultaneous operation could the production order be fulfilled. In these types of Work questions, it helps to determine how much work-time is needed to complete the job. Here, we have 3 machines working 36 hours each... (3 machines)(36 hours each) = 108 machine-hours of work needed to complete the job. Adding 1 additional machine creates the following equation: (4 machines)(X hours each) = 108 machine-hours of work X = 108/4 = 27 hours for each machine The question asks for how many FEWER hours are needed... 36 hours - 27 hours = 9 fewer hours Final Answer: B GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • Magoosh Study with Magoosh GMAT prep 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 • Award-winning private GMAT tutoring Register now and save up to$200

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