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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 ## A draining pipe can empty a pool in 4 hours tagged by: NandishSS ##### This topic has 3 expert replies and 1 member reply ## A draining pipe can empty a pool in 4 hours A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool? A. 9 liters B. 18 liters C. 27 liters D. 36 liters E. 45 liters OA: D[/spoiler] ### GMAT/MBA Expert Senior | Next Rank: 100 Posts Joined 16 Dec 2014 Posted: 94 messages Followed by: 4 members Upvotes: 2 GMAT Score: 770 Top Reply NandishSS wrote: A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool? A. 9 liters B. 18 liters C. 27 liters D. 36 liters E. 45 liters OA: D[/spoiler] C = Capacity of the pool in L R = Rate of drainage in L per hour Work = Rate * Time (1) C = R *4 (we know that the pool can be emptied in 4 hours) (2) C + 3*6 = R*6 (we know that when its raining and an extra 3L is added to the pool an hour the pool is emptied in 6 hours (1) C = 4R (2) C + 18 = 6R 4R + 18 = 6R [put equation (1) into (2) to eliminate C] 2R = 18 R = 9 C = 4*9 [Put R = 9 into equation (1) to work out C] C = 36 Answer is D ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 14929 messages Followed by: 1855 members Upvotes: 13060 GMAT Score: 790 NandishSS wrote: A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool? A. 9 liters B. 18 liters C. 27 liters D. 36 liters E. 45 liters We can PLUG IN THE ANSWERS, which represent the capacity of the pool. When the correct answer is plugged in, the time to empty the pool when the draining pipe and intake pipe work simultaneously = 6 hours. The correct answer is likely to be divisible by the given times and rates (4 hours, 6 hours, 3 liters per hour). Only D is a multiple of 4, 6 and 3. D: 36 liters Since the draining pipe alone takes 4 hours hours to drain the pool, the draining pipe's rate = w/t = 36/4 = 9 liters per hour. Since the draining pipe REMOVES 9 liters per hour, while the intake pipe ADDS 3 liters per hour, the net removal rate when the two pipes operate together = 9-3 = 6 liters per hour. Since the two pipes together have a net removal rate of 6 liters per hour, the time for the two pipes together to empty the 36-liter pool = w/r = 36/6 = 6 hours. Success! The correct answer is D. _________________ 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 09 Apr 2015 Posted: 1461 messages Followed by: 17 members Upvotes: 39 NandishSS wrote: A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool? A. 9 liters B. 18 liters C. 27 liters D. 36 liters E. 45 liters We can let c = the capacity of the pool. We see that the rate of the pipe emptying the pool is c/4 when the pool is full and itâ€™s not raining. and that the rate of the pipe emptying the pool is c/6 when the pool is full and itâ€™s raining. We can create the following equation: c/4 - 3 = c/6 Multiplying the equation by 12, we have: 3c - 36 = 2c c = 36 Answer: D _________________ Jeffrey Miller Head of GMAT Instruction ### Top Member Legendary Member Joined 29 Oct 2017 Posted: 680 messages Followed by: 4 members Hi NandishSS, Let the rate of the draining pipe be xx liters per hour. Then the capacity of the tank will be C = time âˆ- rate = 4x. Now, when raining, the net outflow is x-3 liters per hour, and we are told that at this new rate the pool is emptied in 6 hours. So, the capacity of the pool also equals to C = time âˆ- rate = 6(x-3). Thus we have: 4x = 6(x-3) --> x = 9 --> C = 4x = 36. Option D. 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