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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 ## Greg is training for a marathon by running to and from work tagged by: swerve ##### This topic has 3 expert replies and 0 member replies ### Top Member ## Greg is training for a marathon by running to and from work ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Greg is training for a marathon by running to and from work each day, a distance of 12 miles each way. He runs from home to work at an average speed of 6 miles per hour and returns at an average speed of 4 miles per hour. What is Greg’s average speed, in miles per hour, for the round trip? A. 5.5 B. 5.0 C. 4.8 D. 2.5 E. 2.4 The OA is C. Source: Princeton Review ### GMAT/MBA Expert GMAT Instructor Joined 09 Oct 2010 Posted: 1282 messages Followed by: 29 members Upvotes: 59 swerve wrote: Greg is training for a marathon by running to and from work each day, a distance of 12 miles each way. He runs from home to work at an average speed of 6 miles per hour and returns at an average speed of 4 miles per hour. What is Greg’s average speed, in miles per hour, for the round trip? A. 5.5 B. 5.0 C. 4.8 D. 2.5 E. 2.4 Source: Princeton Review Let´s use UNITS CONTROL, one of the most powerful tools of our method! $$? = {{{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{miles}}} \over {{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}}}$$ $$12\,\,{\rm{miles}}\,\,\,\,\left\{ \matrix{ \,\,{\rm{home - work}}:\,\,\,12\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {\,6\,\,{\rm{miles}}\,}}\matrix{ \nearrow \cr \nearrow \cr } } \right)\,\,\,\,\, = \,\,2\,{\rm{h}} \hfill \cr \,\,{\rm{work - home}}:\,\,\,12\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {\,4\,\,{\rm{miles}}\,}}\matrix{ \nearrow \cr \nearrow \cr } } \right)\,\, = \,\,3\,{\rm{h}} \hfill \cr} \right.\,\,\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}\,\,\, = \,\,5\,\,{\rm{h}}$$ Obs.: arrows indicate licit converters. $$? = {{2 \cdot 12} \over 5} = {{20 + 4} \over 5} = 4{4 \over 5}\,\, = \,\,4.8\,\,\,\,\,\left[ {{\rm{mph}}} \right]$$ 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: 2012 messages Followed by: 14 members Upvotes: 43 swerve wrote: Greg is training for a marathon by running to and from work each day, a distance of 12 miles each way. He runs from home to work at an average speed of 6 miles per hour and returns at an average speed of 4 miles per hour. What is Greg’s average speed, in miles per hour, for the round trip? A. 5.5 B. 5.0 C. 4.8 D. 2.5 E. 2.4 We can use the formula: average rate = total distance/total time: average rate = 24/(12/6 + 12/3) = 24/5 = 4.8 Answer: C _________________ Scott Woodbury-Stewart Founder and CEO ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10071 messages Followed by: 494 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that Greg is training for a marathon by running to and from work each day, a distance of 12 miles each way; he runs from home to work at an average speed of 6 miles per hour and returns at an average speed of 4 miles per hour. We're asked for Greg’s average speed, in miles per hour, for the round trip. 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 Greg is running the SAME distance in each direction, it will take him MORE time travel that distance at 4 miles/hour than it will take him to travel at 6 miles/hour. This makes this a 'Weighted Average' scenario - meaning that his average speed will be CLOSER to 4 miles/hour than it will be to 6 miles/hour. We can eliminate Answers A and B. Since his speed never drops below 4 miles/hour, there's no way for his average speed to be less than that - so we can eliminate Answers D and E. There's only one answer remaining... Final Answer: C GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • FREE GMAT Exam Know how you'd score today for$0

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