• NEW! FREE Beat The GMAT Quizzes
Hundreds of Questions Highly Detailed Reporting Expert Explanations
• 7 CATs FREE!
If you earn 100 Forum Points

Engage in the Beat The GMAT forums to earn
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 Twelve identical machines, running continuously at the same tagged by: AAPL This topic has 4 expert replies and 0 member replies Top Member Twelve identical machines, running continuously at the same Timer 00:00 Your Answer A B C D E Global Stats Difficult Manhattan Prep Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days? A. 2 B. 3 C. 4 D. 6 E. 9 OA C GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 496 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. We're asked how many ADDITIONAL machines, each running at the same constant rate, would be needed to REDUCE the time required to complete a shipment BY two days. In these types of 'work' questions, it often helps to calculate the total amount of work needed, then consider the other variables involved. Here, since we have 12 machines EACH working for 8 days, the total amount of work to complete a shipment would be... (12 machines)(8 days each) = 96 machine-days of work Thus, 1 machine would need 96 days to complete the job 2 machines would need 48 days each to complete the job 3 machines would need 32 days each to complete the job Etc. We're asked to reduce the total time by 2 days, meaning that the job should take 6 days to complete. That would require... (96 machine days of work)/(6 total days) = 16 machines needed, each working for 6 days. We already have 12 machines, so we would need 4 more machines. Final Answer: C GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com GMAT/MBA Expert GMAT Instructor Joined 22 Aug 2016 Posted: 1975 messages Followed by: 30 members Upvotes: 470 AAPL wrote: Manhattan Prep Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days? A. 2 B. 3 C. 4 D. 6 E. 9 OA C It is given that currently, 12 machines complete the work in 8 days and we want the work to be completed within 8 - 2 = 6 days. Since the number of days are reduced by a factor 6/8 = 3/4, we need a greater number of machines, i.e., a total of 12*(4/3) = 16 machines. Thus, the number of additional machines = 16 - 12 = 4. The correct answer: C Hope this helps! -Jay _________________ Manhattan Review GMAT Prep Locations: Manhattan Review Dilsukhnagar | Hyderabad GMAT Prep | Bangalore GMAT Courses | Kukatpally GRE Prep | and many more... Schedule your free consultation with an experienced GMAT Prep Advisor! Click here. GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15348 messages Followed by: 1864 members Upvotes: 13060 GMAT Score: 790 AAPL wrote: Manhattan Prep Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days? A. 2 B. 3 C. 4 D. 6 E. 9 One approach is to use the following equation: (machines)(time) / output = (machines)(time) / output In the equation above: Machines and time are INVERSELY PROPORTIONAL. As the number of machines increases, the amount of time required to produce the same output decreases. Machines and output are DIRECTLY PROPORTIONAL. As the number of machines increases, the amount of output also increases. Time and output are also DIRECTLY PROPORTIONAL. As the amount of time increases, the amount of output also increases. In the problem above: (12 machines)(8 days)/(1 shipment) = (x machines)(6 days)/(1 shipment) 12*8 = 6x 16 = x. Since the number of machines must increase to 16 from 12, the number of additional machines required = 16-12 = 4. The correct answer is C. Similar problem: https://www.beatthegmat.com/work-rate-problem-t297557.html _________________ 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: 2791 messages Followed by: 18 members Upvotes: 43 AAPL wrote: Manhattan Prep Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days? A. 2 B. 3 C. 4 D. 6 E. 9 OA C We are given that 12 machines have a rate of 1/8. We want the shipment to be completed in 6 days, which means that the rate would be 1/6. We need to determine the number of machines necessary to have that rate of 1/6. We can create the following proportion in which n = the new number of machines: 12/(1/8) = n(/1/6) Multiplying the left side by 8/8 and the right side by 6/6, we get: 96 = 6n 16 = n Thus, there would need to be 4 additional machines. 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 • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder 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 • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE 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 • FREE GMAT Exam Know how you'd score today for$0

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

• Award-winning private GMAT tutoring
Register now and save up to \$200

Available with Beat the GMAT members only code

Top First Responders*

1 Ian Stewart 57 first replies
2 Brent@GMATPrepNow 31 first replies
3 Jay@ManhattanReview 29 first replies
4 GMATGuruNY 21 first replies
5 ceilidh.erickson 15 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

Most Active Experts

1 Scott@TargetTestPrep

Target Test Prep

199 posts
2 Max@Math Revolution

Math Revolution

84 posts
3 Brent@GMATPrepNow

GMAT Prep Now Teacher

69 posts
4 Ian Stewart

GMATiX Teacher

65 posts
5 GMATGuruNY

The Princeton Review Teacher

40 posts
See More Top Beat The GMAT Experts