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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 ## Together, 15 type A machines and 7 type B machines can tagged by: M7MBA ##### This topic has 2 expert replies and 0 member replies ### Top Member ## Together, 15 type A machines and 7 type B machines can ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Together, 15 type A machines and 7 type B machines can complete a certain job in 4 hours. Together 8 type B machines and 15 type C machines can complete the same job in 11 hours. How many hours would it take one type A machine, one type B machine, and one type C machine working together to complete the job (assuming constant rates for each machine)? (A) 22 hours (B) 30 hours (C) 44 hours (D) 60 hours (E) It cannot be determined from the information above. OA=C Source: Veritas Prep ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15257 messages Followed by: 1861 members Upvotes: 13060 GMAT Score: 790 Top Reply M7MBA wrote: Together, 15 type A machines and 7 type B machines can complete a certain job in 4 hours. Together 8 type B machines and 15 type C machines can complete the same job in 11 hours. How many hours would it take one type A machine, one type B machine, and one type C machine working together to complete the job (assuming constant rates for each machine)? (A) 22 hours (B) 30 hours (C) 44 hours (D) 60 hours (E) It cannot be determined from the information above. Let the job = 44 units. Since 15A+7B take 4 hours to complete the 44-unit job, the rate for 15A+7B = w/t = 44/4 = 11 units per hour. Since 8B+15C take 11 hours to complete the 44-unit job, the rate for 8B+15C = w/t = 44/11 = 4 units per hour. Adding together 15A+7B=11 and 8B+15C=4, we get: 15A + 15B + 15C = 15 units per hour A+B+C = 1 unit per hour Since the rate for A+B+C = 1 unit per hour, the time for A+B+C to complete the 44-unit job = w/r = 44/1 = 44 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 GMAT Instructor Joined 25 Apr 2015 Posted: 2424 messages Followed by: 18 members Upvotes: 43 M7MBA wrote: Together, 15 type A machines and 7 type B machines can complete a certain job in 4 hours. Together 8 type B machines and 15 type C machines can complete the same job in 11 hours. How many hours would it take one type A machine, one type B machine, and one type C machine working together to complete the job (assuming constant rates for each machine)? (A) 22 hours (B) 30 hours (C) 44 hours (D) 60 hours (E) It cannot be determined from the information above. OA=C Source: Veritas Prep Let a, b, and c be the times, in hours, it takes for 1 type A, B, and C machine to finish the job by itself, respectively. So we can create the equations (notice that, for example, 1/a will be the work done by 1 type A machine per hour and n/a will be the work done by n type A machines per hour): 4(15/a) + 4(7/b) = 1 and 11(8/b) + 11(15/c) = 1 If we divide the first equation by 4 and the second by 11, we have: 15/a + 7/b = 1/4 And 8/b + 15/c = 1/11 Now, adding the two new equations, we have: 15/a + 15/b + 15/c = 1/4 + 1/11 15(1/a + 1/b + 1/c) = 15/44 1/a + 1/b + 1/c = 1/44 Thus, the combined rate of 1 type A, B and C machine is 1/44. That is, together they finish 1/44 of the job in one hour. Therefore, it will take them 1/(1/44) = 44 hours to finish 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 • 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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