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 Author: niheil [ 09 Oct 2010, 12:13 ] Post subject: If car X followed car Y across a certain bridge that is 21-m If car X followed car Y across a certain bridge that is 21-mile long, how many seconds did it take car X to travel across the bridge?(1) Car X drove onto the bridge exactly 3 seconds after car Y drove onto the bridge and drove off the bridge exactly 2 seconds after car Y drove off the bridge.(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour.Additional info on the problemSource: Paper TestTest Code: 42Section: 2 (Data Sufficiency)Problem: 5

 Author: Bunuel [ 09 Oct 2010, 12:43 ] Post subject: Re: Plz Help with Data Sufficiency problem niheil wrote:Hi guys,Please explain how to answer the following Data Sufficiency question:If car X followed car Y across a certain bridge that is 21mile long, how many seconds did it take car X to travel across the bridge?(1) Car X drove onto the bridge exactly 3 seconds after car Y drove onto the bridge and drove off the bridge exactly 2 seconds after car Y drove off the bridge.(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour.Let the time needed for car X to travel across the bridge be $$t_x$$ seconds and the time for Y $$t_y$$ seconds.Question: $$t_x=?$$(1) Car X drove onto the bridge exactly 3 seconds after car Y drove onto the bridge and drove off the bridge exactly 2 seconds after car Y drove off the bridge --> car X needs 1 second less to travel across the bridge than car Y --> $$t_y=t_x+1$$. Not sufficient to calculate $$t_x$$.(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour = $$\frac{30}{3600}=\frac{1}{120}$$ miles per second --> car Y needs $$t_y=\frac{21}{\frac{1}{120}}=21*120$$ seconds to travel across the bridge. Not sufficient to calculate $$t_x$$.(1)+(2) $$t_y=t_x+1$$ and $$t_y=21*120$$ --> $$t_x=21*120-1$$. Sufficient.Answer: C.

 Author: niheil [ 09 Oct 2010, 14:00 ] Post subject: Re: Plz Help with Data Sufficiency problem Awesome! Thanks again, Bunuel. I wish you could take the GMAT for me, lol.

 Author: PennState08 [ 02 Dec 2010, 14:09 ] Post subject: Rate Problem All,This was a data sufficiency problem, but want to double check my math in case I see it in a problem solver.If Car X followed Car Y across a certain bridge that is $$\frac{1}{2}$$ mile long, how many seconds did it take Car X to travel across the bridge?(1) Car X drove onto the bridge exactly 3 seconds after Car Y drove onto the bridge and drove off the bridge exactly 2 seconds after Car Y drove off the bridge.(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour.C is the correct answer for data sufficiency, but I want to go through the problem in various ways (problem solving) to make sure my math is correct.Provided all the data; What are the rates of each Car? How many seconds would it take for Car X to catch Car Y? At what distance would Car X catch Car Y? Rate Car X: ~30.5 mph OR $$\frac{1}{118}$$ miles per secondRate Car Y: 30 mph (given) OR $$\frac{1}{120}$$ miles per secondSecond for Car X to catch Car Y: 180 seconds OR 3 minutes OR $$\frac{1}{20}$$ hourDistance: 1.5 milesExplanations:Rate x Time(t) = DistanceCar Y (given at 30 mph, so find $$t$$ to solve for rate of car X)$$y$$ x $$t$$ = $$\frac{1}{2}$$30 x $$t$$ = $$\frac{1}{2}$$ (need miles per second, not hour)$$\frac{1}{120}$$ x $$t$$ = $$\frac{1}{2}$$$$t$$ = 60 Car X$$x$$ x ($$t$$ - 1) = $$\frac{1}{2}$$ ; 1 second for the time difference (waited 3 seconds after Y, finished 2 seconds after Y: 3 - 2 = 1)$$x$$ x (60 - 1) = $$\frac{1}{2}$$ $$x$$ x 59 = $$\frac{1}{2}$$$$x$$ = $$\frac{1}{118}$$Time (in seconds) Car X catches Car Y:$$\frac{1}{118}$$ ($$t$$ - 3) = $$\frac{1}{120}t$$ ; 3 = amount of seconds after Y left.$$\frac{1}{118} t$$ - $$\frac{3}{118}$$ = $$\frac{1}{120}t$$$$\frac{60}{7080}t$$ - $$\frac{180}{7080}$$ = $$\frac{59}{7080}$$$$\frac{1}{7080} t$$ = $$\frac{180}{7080}$$$$t$$ = 180 seconds180 seconds for Car X to catch Car YDistance (in miles) for Car X to catch Car YTaking either equation and substituting 180 for $$t$$X) $$\frac{1}{118}$$ x (180-3) = 1.5 milesY) $$\frac{1}{120}$$ x (180) = 1.5 milesI have all this set up correctly, right?

 Author: Bunuel [ 02 Dec 2010, 14:20 ] Post subject: Re: Rate Problem Merging similar topics. The only difference is in the length of the bridge (21 miles in first question and 1/2 miles in the second one). But the answer for both of them is C. Please ask if anything remains unclear.

 Author: Basshead [ 13 Oct 2020, 09:37 ] Post subject: Re: If car X followed car Y across a certain bridge that is 21-m (1) This tells us Car X crosses the bridge 1 second faster than Car Y. We can't determine the time it took for Car X to cross the bridge.(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour. We can determine the time it takes Car Y to cross the bridge; however, this does not tell us anything about Car X(1 & 2) From Statement 2 we can determine the time it takes Car Y to cross the bridge. We know Car X crosses the bridge 1 second faster than Car Y. Therefore, with both statements, we can determine the time it takes Car X to cross the bridge.

 Author: Hoozan [ 25 May 2021, 00:52 ] Post subject: Re: If car X followed car Y across a certain bridge that is 21-m EducationAisle based on (1) doesn't car X take 5 seconds longer that car Y? Why is this not correct?

 Author: EducationAisle [ 25 May 2021, 02:52 ] Post subject: Re: If car X followed car Y across a certain bridge that is 21-m Hoozan wrote:EducationAisle based on (1) doesn't car X take 5 seconds longer that car Y? Why is this not correct?Not really 5 seconds Hoozan. Car X a) drove onto the bridge exactly 3 seconds after car Y drove onto the bridge and b) drove off the bridge exactly 2 seconds after car Y drove off the bridge.Notice that if X and Y had same speeds, then X would have driven off the bridge exactly 3 seconds after car Y drove off the bridge (because X drove onto the bridge exactly 3 seconds after car Y drove onto the bridge).However, since X drove drove off the bridge exactly 2 seconds after car Y drove off the bridge, this would mean that X "caught up" with Y, 1 second, on the bridge. So, car X actually took 1 second less than car Y, to travel the bridge.

 Author: bumpbot [ 03 Aug 2022, 10:11 ] Post subject: Re: If car X followed car Y across a certain bridge that is 21-m Hello from the GMAT Club BumpBot!Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.

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