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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 ## Mechanics Question ##### This topic has 2 expert replies and 23 member replies Goto page • 1, • 2 ## Mechanics Question Richard began driving from home on a trip averaging 30 miles per hour. How many miles per hour must Carla drive on average to catch up to him in exactly 3 hours if she leaves 30 minutes after Richard? - 35 - 55 - 39 - 40 - 60 Senior | Next Rank: 100 Posts Joined 25 Jun 2010 Posted: 74 messages Upvotes: 3 .A distance driven by R = 30 * 3hours = 90 miles C has to drive 90 miles in 2.5 hours to catch upto R. 90 = Rate * 2.5 ; Rate = 36. Master | Next Rank: 500 Posts Joined 16 Oct 2010 Posted: 182 messages Upvotes: 4 Hey thanks for your reply! If you don't mind can you explain from where did you get the 2.5 hours? Also 36 isn't one of the given answers? Should we approximate or what? Master | Next Rank: 500 Posts Joined 26 Aug 2010 Posted: 154 messages Followed by: 19 members Upvotes: 46 Test Date: Dec. 2010 Target GMAT Score: 700+ GMAT Score: 760 Carla left 30 minutes after Richard. Richard is traveling 30 miles per hour. That means when Carla started Richard was 15 miles ahead of her. Carla needs to drive at a speed that will allow her to make up those fifteen miles in three hours. To travel 15 miles in three hours would require a rate of 5 mph. But remember Richard is still traveling at 30 mph so you have to add the 5 mph to Richard's speed of 30 mph. Thus, the answer is 35 mph. Hope this helps... Master | Next Rank: 500 Posts Joined 26 Aug 2010 Posted: 154 messages Followed by: 19 members Upvotes: 46 Test Date: Dec. 2010 Target GMAT Score: 700+ GMAT Score: 760 vijaynaik wrote: .A distance driven by R = 30 * 3hours = 90 miles C has to drive 90 miles in 2.5 hours to catch upto R. 90 = Rate * 2.5 ; Rate = 36. This problem can also be solved this by this method. Carla drives for exactly 3 hours. Richard drives for an additional 30 minutes, so his total time is 3.5 hours. Richard drives at 30 mph so his total distance is 105 miles. Carla needs to drive 105 miles in 3 hours or 35 mph. All of these problems use some form of the equation: Distance = Rate X Time Master | Next Rank: 500 Posts Joined 16 Oct 2010 Posted: 182 messages Upvotes: 4 Yep thanks for explaining mate. I had a problem understanding the wording in the problem but it's clear now. thanks again Have a great day Master | Next Rank: 500 Posts Joined 19 Jul 2010 Posted: 126 messages Upvotes: 6 N:Dure wrote: Richard began driving from home on a trip averaging 30 miles per hour. How many miles per hour must Carla drive on average to catch up to him in exactly 3 hours if she leaves 30 minutes after Richard? - 35 - 55 - 39 - 40 - 60 The method of Relative Speed works best here: In 30 mins, Richard has covered = 15 miles... So, now Carla needs to cover 15miles in 3 hours... Hence use the simple D = R * T, -> 15/(x-30)=3... we use x-30 coz they are travelling in the same direction... solve x = 35... Hope it Helped Senior | Next Rank: 100 Posts Joined 15 Jan 2011 Posted: 43 messages Upvotes: 9 N:Dure wrote: Richard began driving from home on a trip averaging 30 miles per hour. How many miles per hour must Carla drive on average to catch up to him in exactly 3 hours if she leaves 30 minutes after Richard? - 35 - 55 - 39 - 40 - 60 I find the easiest way to deal with these kinds of problems is to set up R X T = D tables. RATE (m/hr) X TIME (Hrs) = DISTANCE Richard 30 X 3.5 = 105 Carla ?? X 3.0 = 105 The distance for R and C should be idential at 105m. We need to solve for Carla's speed i.e., ?? Carla will catch Richard in 3 hours (105m) if she travels at 105/3.0 = 35m/hr Therefore the correct answer is A = 35 Master | Next Rank: 500 Posts Joined 06 Nov 2010 Posted: 143 messages Followed by: 1 members Upvotes: 10 Test Date: Oct 8 N:Dure wrote: Richard began driving from home on a trip averaging 30 miles per hour. How many miles per hour must Carla drive on average to catch up to him in exactly 3 hours if she leaves 30 minutes after Richard? - 35 - 55 - 39 - 40 - 60 Richard: Rate: 30mph; Time: 3.5 (since we have 3 hours + 30 minutes); Distance: 30*3.5 Carla: Rate: R; Time: 3 (since she left 30 minutes after Richard); Distance: 3R We want Carla to catch up to Richard, so we need to find out how fast Carla needs to travel to equal the distance Richard has traveled. So, Carla = Richard 30(3.5) = 3R 105 = 3R R = 35 Senior | Next Rank: 100 Posts Joined 27 Mar 2011 Posted: 40 messages Upvotes: 2 in 30 min Rich covers = 15 miles So in 3 hrs Carla has to cover 15 miles extra i.e. 5 miles every hr. So her speed should be 30 + 5 =35 hence A. Master | Next Rank: 500 Posts Joined 24 May 2011 Posted: 401 messages Followed by: 5 members Upvotes: 37 N:Dure wrote: Richard began driving from home on a trip averaging 30 miles per hour. How many miles per hour must Carla drive on average to catch up to him in exactly 3 hours if she leaves 30 minutes after Richard? - 35 - 55 - 39 - 40 - 60 in 3.5 hrs richard drove 105 miles to catch up, 105/3 = 35 m/hr Master | Next Rank: 500 Posts Joined 31 May 2011 Posted: 123 messages Followed by: 1 members Upvotes: 5 Target GMAT Score: 700+ IMO A _________________ Nikhil K Jain ____________________ "Life is all about timing" Don't waste your and others time. Newbie | Next Rank: 10 Posts Joined 23 Sep 2011 Posted: 2 messages I like to look at this one from a slightly different perspective. Richard left 30 mins before Carla so will have travelled for 3.5 hours when they meet. 3.5hrs x 30 miles an hour = 105 miles covered Carla must travel 105 miles in 3 hours to catch Richard. 105/3hrs = 35mph Master | Next Rank: 500 Posts Joined 08 Dec 2010 Posted: 425 messages Followed by: 7 members Upvotes: 56 GMAT Score: 690 "catch up" means, that C and R drove the same distance when they met. So, we have 3*x=30*(3+1/2) (1/2 is 30min/60 min=1/2 h) x=35 C's speed is 35 Legendary Member Joined 23 Dec 2011 Posted: 626 messages Followed by: 10 members Upvotes: 31 Test Date: June Target GMAT Score: 750 If x miles/hr is speed, x*(3) = 30*(3+1/2) => x = 35 _________________ Follow your passion, Success as perceived by others shall follow you • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep 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 • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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