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Register now and save up to $200 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 • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code ## It would take one machine 4 hours (OG16) This topic has 1 expert reply and 1 member reply boomgoesthegmat Senior | Next Rank: 100 Posts Joined 25 Apr 2016 Posted: 93 messages Thanked: 1 times #### It would take one machine 4 hours (OG16) Thu May 19, 2016 3:46 pm Elapsed Time: 00:00 • Lap #[LAPCOUNT] ([LAPTIME]) It would take one machine 4 hours to complete a large production order and another machine 3 hours to complete the same order. How many hours would it take both machines, working simultaneously at their respective constant rates, to complete the order? A) 7/12 B) 1 1/2 C) 1 5/7 D) 3 1/2 E) 7 OA: C Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums! ### GMAT/MBA Expert Rich.C@EMPOWERgmat.com Elite Legendary Member Joined 23 Jun 2013 Posted: 8699 messages Followed by: 460 members Thanked: 2729 times GMAT Score: 800 Thu May 19, 2016 4:41 pm Hi boomgoesthegmat, In "work" questions, there are 2 common ways to get to the correct answer (although there are several different ways to "do the math"): 1) When there are 2 entities (people, machines, etc.) working on a task together, use the Work Formula. 2) Convert the individual rates of the 2 (or more) entities, combine and be sure to answer the question that's asked. In this question, here's how you could use the two options mentioned: We're told... Machine A = 4 hours to complete an order Machine B = 3 hours to complete the same order We're asked how long it would take the two machines, WORKING TOGETHER, to complete the order. 1) Using the Work Formula: (A)(B)/(A+B)..... (4)(3)/(4+3) = 12/7 hours to complete the job 2) Using the individual rates: Machine A: 4 hours to do the entire job --> 1 hour to do 1/4 of the job Machine B: 3 hours to do the entire job --> 1 hour to do 1/3 of the job In 1 hour, 1/4 + 1/3 = 7/12 of the job is done **Note: this calculation tells you the FRACTION of the JOB that is complete in 1 HOUR** Since there is 1 job to complete.....1/(7/12) = 12/7 hours to complete the job Either way, the Final Answer is...C GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com OptimusPrep Master | Next Rank: 500 Posts Joined 13 Mar 2015 Posted: 410 messages Followed by: 7 members Thanked: 120 times GMAT Score: 770 Thu May 19, 2016 8:11 pm boomgoesthegmat wrote: It would take one machine 4 hours to complete a large production order and another machine 3 hours to complete the same order. How many hours would it take both machines, working simultaneously at their respective constant rates, to complete the order? A) 7/12 B) 1 1/2 C) 1 5/7 D) 3 1/2 E) 7 OA: C Assume total work = 12 units (LCM of both the times) Work rate of machine 1 = 3 units/hr Work rate of machine 2 = 4 units/hr Total work = 12 units. Total work rate when both machines work together = 7 units/hr Hence the work would be completed in 12/7 hr = 1 5/7 hrs Correct Option: C _________________ Ankur 99th Percentile GMAT Tutor | Optimus Prep™ Optimus Prep™ GMAT Courses: www.Optimus-Prep.com/GMAT Free Online Trial Hour: http://www.optimus-prep.com/request-free-online-trial-hour/ Free GMAT Study Plan: http://www.optimus-prep.com/ebook/ Optimus Prep™ Rates: GMAT Private Tutoring Online:$80-100/hr.*
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