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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 ## Working alone, pump A can empty a pool in 3 hours. Working tagged by: BTGmoderatorLU ##### This topic has 2 expert replies and 1 member reply ### Top Member ## Working alone, pump A can empty a pool in 3 hours. Working ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Source: Magoosh Working alone, pump A can empty a pool in 3 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool? A. 72 B. 75 C. 84 D. 96 E. 108 The OA is A. ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 9840 messages Followed by: 490 members Upvotes: 2867 GMAT Score: 800 Top Reply Hi All, We're told that working alone, Pump A can empty a pool in 3 HOURS and Pump B can empty the same pool in 2 HOURS. We're asked how many MINUTES it would take the two pumps, working together, to empty the pool. This question can be solved in a couple of different ways, including with the Work Formula: Work = (A)(B)/(A+B) where A and B are the 2 individual times it takes to complete the task Since Pump A can empty the pool in 3 hours and Pump B can empty the pool in 2 hours, it would take (3)(2)/(3+2) = 6/5 to drain the pool. Since 1/5 of an hour is 12 minutes, the total time would be 60 + 12 = 72 minutes to empty the pool. Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com ### Top Member Legendary Member Joined 02 Mar 2018 Posted: 608 messages Followed by: 1 members If pump A can empty pool in 3 hours $$In\ 1\ hour\ it\ will\ empty\ \frac{1}{3}of\ the\ pool$$ If pump B can empty the pool in 2 hours, $$In\ 1\ hour\ it\ will\ empty\ \frac{1}{2}of\ the\ pool$$ By working together their work rate per hour = $$=\ \frac{1}{3}+\frac{1}{2}$$ $$=\frac{\left(2+3\right)}{6}=\ \frac{5}{6}of\ the\ pool\ per\ hour$$ 1 hour = 60 minutes. $$If\ the\ two\ pumps\ can\ empty\ \frac{5}{6}of\ the\ pool\ in\ 60\ \min utes,\ how\ many\ \min utes\ will\ it\ take\ for\ them\ to\ empty\ the\ whole\ pool\ completely.$$ $$\frac{5}{6}=60\ \min utes$$ $$1\ =\ x$$ $$\frac{5}{6}x\ =60\ \cdot\ 1$$ $$x\ =\ \frac{60}{\frac{5}{6}}$$ $$x=\frac{60\cdot6}{5}\ =\ \frac{360}{5}=72$$ Option A is CORRECT. ### GMAT/MBA Expert GMAT Instructor Joined 25 Apr 2015 Posted: 1649 messages Followed by: 14 members Upvotes: 43 BTGmoderatorLU wrote: Source: Magoosh Working alone, pump A can empty a pool in 3 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool? A. 72 B. 75 C. 84 D. 96 E. 108 The combined rate of pumps A and B is: 1/3 + 1/2 = 2/6 + 3/6 = 5/6, so the time is 1/(5/6) = 6/5 hours, which is 6/5 x 60 = 72 minutes. Answer: A _________________ Scott Woodbury-Stewart Founder and CEO • 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 • Magoosh Study with Magoosh GMAT prep 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 • Award-winning private GMAT tutoring Register now and save up to$200

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