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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 ## Vivian drives to her sister's house and back. She takes the tagged by: AAPL ##### This topic has 5 expert replies and 0 member replies ### Top Member ## Vivian drives to her sister's house and back. She takes the ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Princeton Review Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour? A. 50 B. 58.3 C. 60 D. 61.7 E. 70 OA B ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12735 messages Followed by: 1246 members Upvotes: 5254 GMAT Score: 770 AAPL wrote: Princeton Review Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour? A. 50 B. 58.3 C. 60 D. 61.7 E. 70 One approach is to assign a "nice" value (one that works well with 50 mph and 70 mph) to the distance her sister's house. So, let's say the distance is 350 miles Average speed = (total distance traveled)/(total travel time) TOTAL distance = 350 miles + 350 miles = 700 miles Now let's calculate the TOTAL travel time. time = distance/speed So, travel time TO her sister's house = 350/50 = 7 hours And travel time FROM her sister's house = 350/70 = 5 hours So, TOTAL travel time = 7 hours + 5 hours = 12 hours So, average speed = 700 miles/12 hours = 700/12 miles per hour = 350/6 miles per hour = 175/3 miles per hour = 58 1/3 miles per hour ≈ 58.3333 miles per hour Answer: B _________________ Brent Hanneson – Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15192 messages Followed by: 1860 members Upvotes: 13060 GMAT Score: 790 AAPL wrote: Princeton Review Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour? A. 50 B. 58.3 C. 60 D. 61.7 E. 70 When the same distance is traveled at two different speeds, the average speed for the entire trip will be a bit LESS than the average of the two speeds. Since (70+50)/2 = 60, the average speed for Vivian's's entire trip must be a bit less than 60. The correct answer is B. _________________ 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 Oct 2010 Posted: 1434 messages Followed by: 31 members Upvotes: 59 AAPL wrote: Princeton Review Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour? A. 50 B. 58.3 C. 60 D. 61.7 E. 70 Alternate way: UNITS CONTROL, one of the most powerful tools of our method! $$? = {{{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{miles}}} \over {{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}}}$$ $$350\,\,{\rm{miles}}\,\,\left( {{\rm{arbitrary!}}} \right)\,\,\,\left\{ \matrix{ \,{\rm{out}}:\,\,350\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {50\,\,{\rm{miles}}}}\matrix{ \nearrow \cr \nearrow \cr } } \right)\,\,\,\,\, = \,\,7\,{\rm{h}} \hfill \cr \,{\rm{back}}:\,\,350\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {70\,\,{\rm{miles}}}}\matrix{ \nearrow \cr \nearrow \cr } } \right)\,\, = \,\,5\,{\rm{h}} \hfill \cr} \right.\,\,\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}\,\, = \,12\,{\rm{h}}$$ Obs.: arrows indicate licit converters. $$? = {{2 \cdot 350} \over {12}} = {{300 + 48 + 2} \over 6} = 58{1 \over 3}\,\,\,\left[ {{\rm{mph}}} \right]$$ This solution follows the notations and rationale taught in the GMATH method. Regards, Fabio. _________________ Fabio Skilnik :: GMATH method creator ( Math for the GMAT) English-speakers :: https://www.gmath.net Portuguese-speakers :: https://www.gmath.com.br ### GMAT/MBA Expert GMAT Instructor Joined 25 Apr 2015 Posted: 2215 messages Followed by: 17 members Upvotes: 43 AAPL wrote: Princeton Review Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour? A. 50 B. 58.3 C. 60 D. 61.7 E. 70 We can let d = the distance one way and use the formula: average rate = total distance/total time: average rate = 2d/(d/50 + d/70) average rate = 2d/(7d/350 + 5d/350) average rate = 2d/(12d/350) average rate = 700d/(12d) = 58.3 Answer: B _________________ Scott Woodbury-Stewart Founder and CEO ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10106 messages Followed by: 494 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that Vivian drives to her sister's house and back. She takes the exact same route both ways; on the trip out she drives an average speed of 50 miles per hour and on the trip back she drives an average speed of 70 miles per hour. We're asked for her approximate average speed for the round trip in miles per hour. This question can be solved in a couple of different ways. Sometimes that answer choices are 'spread out' in such a way that you can avoid almost all of the 'math' and use a 'logic shortcut' to get to the correct answer. To start, since Vivian is driving the SAME distance in each direction, it will take her MORE time travel that distance at 50 miles/hour than it will take her to travel at 70 miles/hour. This makes this a 'Weighted Average' scenario - meaning that her average speed will be CLOSER to 50 miles/hour than it will be to 70 miles/hour. We can eliminate Answers C, D and E. We also know that she travels at 70 miles/hour for some of the trip, so her average cannot be 50 miles/hour (logically, the speed must be greater than that), so we can eliminate Answer A. There's only one answer remaining... Final Answer: B GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE 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 • FREE GMAT Exam Know how you'd score today for$0

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