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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 ## If two trains ,travelling at a speed of 72mph and 48 mph. . tagged by: M7MBA ##### This topic has 3 expert replies and 1 member reply ### Top Member ## If two trains ,travelling at a speed of 72mph and 48 mph. . If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ? A)2 miles B)3 miles C)4 miles D)5 miles E)none of the above. The OA is A. I don't know how to solve this PS question. Experts, could you tell me how? Please. ### Top Member Master | Next Rank: 500 Posts Joined 15 Oct 2009 Posted: 331 messages Upvotes: 27 M7MBA wrote: If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ? A)2 miles B)3 miles C)4 miles D)5 miles E)none of the above. The OA is A. I don't know how to solve this PS question. Experts, could you tell me how? Please. They are approaching each other at a combined speed of 72+48 = 120 mph = 2 miles/minute. So, since they are 1 minute apart according to the question, at their combined speed of 2 miles/minute: distance = rate x time > = 2 miles/minute x 1minute = 2 miles A ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Hello M7MBA. It is easier and faster as regor60 said. But if you don't know about the combine speed, you can solve it as follows. Train A travels at 48mph, which is equivalent to 48/60=4/5 miles per minute. Train B travels at 72mph, which is equivalent to 72/60=6/5 miles per minute. Suppose that you're in the place where they collisioned. If you go back 1 minute, then train A move back 4/5 miles and train B moves back 6/5 miles. So, their distance is equal to 4/5+6/5=10/5=2 miles. So, the correct answer is A. I hope this explanation may help you. I'm available if you'd like a follow up. _________________ GMAT Prep From The Economist We offer 70+ point score improvement money back guarantee. Our average student improves 98 points. Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now. ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 13046 messages Followed by: 1253 members Upvotes: 5254 GMAT Score: 770 M7MBA wrote: If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ? A)2 miles B)3 miles C)4 miles D)5 miles E)none of the above. I call this a shrinking gap question. When we ADD the speeds of the trains, we get 72 mph + 48 mph = 120 mph This means, the gap SHRINKS at a rate of 120 miles per HOUR We can also say that the gap SHRINKS at a rate of 2 miles per MINUTE What is the distance between them 1 minute before the collision ? Since the gap SHRINKS at a rate of 2 miles per MINUTE, we can conclude that, 1 minute before the collision, the trains will be 2 miles apart. Answer: A Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use my video course along with Sign up for free Question of the Day emails And check out all of these free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15388 messages Followed by: 1872 members Upvotes: 13060 GMAT Score: 790 M7MBA wrote: If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ? A)2 miles B)3 miles C)4 miles D)5 miles E)none of the above. Since the trains travel toward each other, they WORK TOGETHER to cover the distance between them. When elements work together, ADD THEIR RATES. Combined rate for the two trains = 72+48 = 120 miles per hour = 2 miles per minute. Let the TOTAL travel time for the two trains = 1 minute. Let the faster train start at Point A and the slower train start at Point B. The question stem becomes: If it takes 1 minute for the two trains to meet, what is the distance between Point A and Point B? Since the two trains travel at a combined rate of 2 miles per minute for a total time of 1 minute, the distance between Point A and Point B = rt = 2*1 = 2 miles. The correct answer is A. _________________ 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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