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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 Tom drives from town A to town B, driving at a constant spee This topic has 4 expert replies and 0 member replies Top Member Tom drives from town A to town B, driving at a constant spee Timer 00:00 Your Answer A B C D E Global Stats Difficult Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour? A. 12 B. 20 C. 24 D. 30 E. 36 OA B Source: Economist GMAT GMAT/MBA Expert GMAT Instructor Joined 25 Apr 2015 Posted: 2852 messages Followed by: 18 members Upvotes: 43 Top Reply BTGmoderatorDC wrote: Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour? A. 12 B. 20 C. 24 D. 30 E. 36 OA B Source: Economist GMAT We can let the distance between B and C = d, and thus the distance between A and B = 2d. We can let r = Tom's speed driving from B to C, in miles per hour, and create the equation: (2d + d)/(2d/60 + d/r) = 36 3d/(d/30 + d/r) = 36 3d = 36d/30 + 36d/r 3 = 6/5 + 36/r Multiplying both sides of the equation by 5r, we have: 15r = 6r + 180 9r = 180 r = 20 Answer: B _________________ 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 GMAT/MBA Expert GMAT Instructor Joined 09 Oct 2010 Posted: 1449 messages Followed by: 32 members Upvotes: 59 Top Reply BTGmoderatorDC wrote: Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour? A. 12 B. 20 C. 24 D. 30 E. 36 Source: Economist GMAT Perfect opportunity for UNITS CONTROL, one of the most powerful tools of our method! $$LCM\left( {36,60} \right) = 180\,\,\,\,\left\{ \matrix{ \,A \to C\,\,\,:\,\,\,180\,\,{\rm{miles}}\,\,\,\left( {{{1\,\,{\rm{hour}}} \over {36\,\,{\rm{miles}}}}} \right)\,\,\,\,\, = \,\,\,5\,\,{\rm{hours}}\, \hfill \cr \,A \to B\,\,\,:\,\,\,{2 \over 3}\left( {180\,\,{\rm{miles}}} \right)\left( {{{1\,\,{\rm{hour}}} \over {60\,\,{\rm{miles}}}}} \right)\,\,\, = \,\,2\,\,{\rm{hours}}\,\,\, \hfill \cr B \to C\,\,\,:\,\,\,\,\,\,\,\,?\,\, = \,\,{{{1 \over 3}\left( {180\,\,{\rm{miles}}} \right)} \over {5 - 2\,\,{\rm{hours}}}}\,\,\, = \,\,\,\,20\,\,{\rm{mph}} \hfill \cr} \right.\,\,\,$$ This solution follows the notations and rationale taught in the GMATH course. 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 22 Aug 2016 Posted: 1984 messages Followed by: 30 members Upvotes: 470 BTGmoderatorDC wrote: Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour? A. 12 B. 20 C. 24 D. 30 E. 36 OA B Source: Economist GMAT A -------------(60 mph)----------2d miles ------------B-----(x mph)-----d miles ------C Given the average speed from A to C = 36, we have Time take to cover the distance from A to C = (2d + d)/36 = d/12 hours Time take to cover the distance from A to B = (2d)/60 = d/30 hours Time take to cover the distance from B to C = d/x hours Thus, d/30 + d/x = d/12 1/30 + 1/x = 1/12 1/x = 1/12 - 1/30 = (5 - 2)/60 = 3/60 = 1/20 => x = 20 mph. The correct answer: B Hope this helps! -Jay _________________ Manhattan Review GMAT Prep Locations: Manhattan Review New Delhi | Hyderabad | GRE Prep Chennai | Madhapur GRE Coaching | 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: 15362 messages Followed by: 1866 members Upvotes: 13060 GMAT Score: 790 BTGmoderatorDC wrote: Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour? A. 12 B. 20 C. 24 D. 30 E. 36 Let the distance between A and B = 120 miles. Since the 120-mile distance between A and B is twice the distance between B and C, the distance between B and C = 60 miles, implying that the total distance = 120+60 = 180 miles. Since the average speed for the 120-mile leg between A and B = 60 mph, the time to travel from A to B = d/r = 120/60 = 2 hours. Since the average speed for the entire 180-mile trip = 36 mph, the time to travel the entire trip = d/r = 180/36 = 5 hours. Time to travel from B to C = (time for the entire trip) - (time to travel from A to B) = 5-2 = 3 hours. Since it takes 3 hours to travel the 60-mile leg between B and C, the driving speed from B to C = d/t = 60/3 = 20 mph. 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! 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