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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 ## Machine A and B ##### This topic has 4 expert replies and 1 member reply ### Top Member ## Machine A and B Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job? A. 12hrs B. 16hrs C. 24hrs D. 28hrs E. 32hrs Is there a strategic approach to this? Experts help please. Thanks OA C ### GMAT/MBA Expert GMAT Instructor Joined 25 Apr 2015 Posted: 2852 messages Followed by: 18 members Upvotes: 43 Top Reply lheiannie07 wrote: Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job? A. 12hrs B. 16hrs C. 24hrs D. 28hrs E. 32hrs The rate of Machine A is 1/24, so in 8 hours, 1/3 of the job is completed, and thus 2/3 of the job is left to be completed. If the rate of Machine B is 2/3 that of Machine A, then the rate of Machine B is (2/3)(1/24) = 1/36. Thus, it will take Machine B (2/3)/(1/36) = 2/3 x 36 = 24 hours to complete the rest of the job. Answer: C _________________ Scott Woodbury-Stewart Founder and CEO scott@targettestprep.com See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15362 messages Followed by: 1866 members Upvotes: 13060 GMAT Score: 790 Top Reply lheiannie07 wrote: Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job? A. 12hrs B. 16hrs C. 24hrs D. 28hrs E. 32hrs Let the job = 72 widgets. Since A takes 24 hours to complete the job, A's rate = w/t = 72/24 = 3 widgets per hour. At a rate of 3 widgets per hour, the work produced by A in 8 hours = rt = 3*8 = 24 widgets. Remaining work = 72-24 = 48 widgets. Since B's rate is 2/3 of A's rate, B's rate = (2/3)(3) = 2 widgets per hour. At a rate of 2 widgets per hour, the time for B to produce the remaining 48 widgets = w/r = 48/2 = 24 hours. The correct answer is C. _________________ 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. ### GMAT/MBA Expert Legendary Member Joined 14 Jan 2015 Posted: 2667 messages Followed by: 122 members Upvotes: 1153 GMAT Score: 770 lheiannie07 wrote: Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job? A. 12hrs B. 16hrs C. 24hrs D. 28hrs E. 32hrs Is there a strategic approach to this? Experts help please. Thanks OA C If machine A can complete the job in 24 hours, and it works for 8 hours, then it has completed 8/24 or 1/3 of the job, leaving 2/3 of the job for B to complete. If Machine A's rate was 1 job/24 hours, or 1/24, and B's rate is 2/3 of this, then B's rate is (2/3) * (1/24) = 1/36. If Machine B works for T hours at a rate of 1/36 and must complete 2/3 of a job, we get the following equation: (1/36) * T = 2/3 --> T = 24; The answer is C _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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lheiannie07 wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs

Is there a strategic approach to this? Experts help please. Thanks

OA C
Another approach. If Machine A has worked for 8 hours, and it takes Machine A 24 hours to complete the job, it would take Machine A an additional 16 hours to finish the job alone.

Rate and Time have a reciprocal relationship. If B's rate is 2/3 of A's rate, then it would take B 3/2 of A's Time to complete the job. If it would have taken A 16 hours to complete the job, it would take B 16*(3/2) or 24 hours. The answer is C.

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Save $100 off any live Veritas Prep GMAT Course Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now! ### Top Member Moderator Joined 07 Sep 2017 Posted: 3052 messages Followed by: 6 members Thank you so much for the solution, but is there an easier way to solve this? • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 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 • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 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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