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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 ## How many hours did it take Helen to drive from her house to tagged by: AAPL ##### This topic has 1 expert reply and 0 member replies ### Top Member ## How many hours did it take Helen to drive from her house to ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult GMAT Prep How many hours did it take Helen to drive from her house to her parent's house? 1) Helen's average speed on this trip was 72 kilometers per hour 2) If Helen's average speed on this trip had been 8 kilometers per hour greater, it would have taken her 1 hour less. OA C ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 15348 messages Followed by: 1864 members Upvotes: 13060 GMAT Score: 790 AAPL wrote: GMAT Prep How many hours did it take Helen to drive from her house to her parent's house? 1) Helen's average speed on this trip was 72 kilometers per hour 2) If Helen's average speed on this trip had been 8 kilometers per hour greater, it would have taken her 1 hour less. Statement 1: If d=72, then t = d/r = 72/72 = 1 hour. If d=144, then t = 144/72 = 2 hours. Since the time can be different values, INSUFFICIENT. Statement 2: Time and rate have a RECIPROCAL RELATIONSHIP: If the time is cut in HALF, then the rate DOUBLES. If the time DOUBLES, then the rate is cut in HALF. Case 1: r = 72 mph Here, 8mph faster = 72+8 = 80mph, yielding the following ratio: (faster rate)/(slower rate) = 80/72 = 10/9. Since rate and time have a reciprocal relationship, we get: (faster time)/(slower time) = 9/10. Implication: Since the faster time is 9/10 of the actual time -- 1/10 less than the actual time -- the 1 hour saved at the faster time is equal to 1/10 of the actual time: 1 = (1/10)t t = 10 hours. Case 1: r = 16 mph Here, 8mph faster = 16+8 = 24mph, yielding the following ratio: (faster rate)/(slower rate) = 24/16 = 3/2. Since rate and time have a reciprocal relationship, we get: (faster time)/(slower time) = 2/3. Implication: Since the faster time is 2/3 of the actual time -- 1/3 less than the actual time -- the 1 hour saved at the faster time is equal to 1/3 of the actual time: 1 = (1/3)t t = 3 hours. Since the time can be different values, INSUFFICIENT. Statements combined: Only Case 1 satisfies both statements, with the result that t = 10 hours. SUFFICIENT. The correct answer is C. _________________ 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. • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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