Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
May 1211:00 AM PDT
-12:00 PM PDT
Ready to test your GRE vocabulary skills in a fun and competitive live setting? Join our interactive GRE Vocabulary Quiz LIVE on YouTube! In this special session, you'll tackle 20 GRE-level vocabulary questions under timed conditions- May 14
08:30 AM PDT
-09:30 AM PDT
Struggling with Boldface or Paradox questions in GMAT Critical Reasoning (CR)? Boldface and Paradox CR questions are often overlooked amidst the other more common GMAT CR question types. But mastering these can significantly boost your Verbal score. - May 14
10:00 AM PDT
-11:00 AM PDT
GMAT Verbal Practice question quiz. Solve 20 GMAT Focus practice questions written by GMAT Ninja. Take this GMAT practice test live with peers in timed conditions, analyze your GMAT study progress, and see where you stand in the GMAT student pool. 
May 1411:30 AM EDT
-12:30 PM EDT
Is INSEAD your dream b-school and you're looking for solid prep and application strategies to get there? Check out Barkavi’s end-to-end journey to know how she did! Get insights into the INSEAD admissions process, know what Adcoms look at, and more!- May 15
10:00 AM PDT
-11:00 AM PDT
Struggling to finish the GMAT on time? You’re not alone. The #1 reason students score lower than expected on the GMAT isn’t lack of knowledge or silly mistakes—it’s running out of time. 
May 1609:00 PM PDT
-10:00 PM PDT
Full-length FE mock with insightful analytics, weakness diagnosis, and video explanations!
May 1711:00 AM IST
-01:00 PM IST
Attend this session to learn how to Deconstruct arguments, Pre-Think Author’s Assumptions, and apply Negation Test.- May 18
11:00 AM IST
-01:00 PM IST
Attend this free GMAT Algebra Webinar and learn how to master the most challenging Inequalities and Absolute Value problems with ease. - Jun 10
06:00 AM PDT
-05:30 PM PDT
Register for the GMAT Club Virtual MBA Spotlight fair, the biggest MBA fair of the year. You will have a chance to hear Admissions directors from almost every Top 20 program speak, network with peers, and conveniently attend morning or afternoon sessions.
29 Sep 2009, 11:55
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
63% (02:10) correct
37%
(02:26)
wrong
based on 516
sessions
History
Date
Time
Result
Not Attempted Yet
Two trains of length 100m and 250m run on parallel lines. when they run in the same direction it will take 70 sec to cross each other and when they run in opposite direction, they take 10 sec to cross each other. Find the speed of faster train.
A. 10 m/s
B. 15 m/s
C. 20 m/s
D. 25 m/s
E. 30 m/s
A. 10 m/s
B. 15 m/s
C. 20 m/s
D. 25 m/s
E. 30 m/s
29 Sep 2009, 13:01
Kudos
Bookmarks
The answer is 20 m/s.
Let the faster train run at x m/s and the slower train run at y m/s.
The first statement states that it will take 70 seconds to cross each other running in the same direction. The first important thing her is that the faster train is behind the slower train, otherwise they would never cross. Secondly, in order to cross the slower train, the faster train will need to cover 350m MORE (250 m + 100 m) in the 70 seconds than the other train.
\(\frac{350}{(x - y)} = 70\)
\(\frac{5}{(x - y)} = 1\)
\(5 = x - y\) (Equation 1)
The second statement states that it will take 10 seconds to cross each other running in the opposite direction. The difference between this and running in the same direction, is that the slower train's speed CONTRIBUTES to the cross rather than inhibiting it. If the slower train was standing still, the faster train would take (350/x) seconds to pass it. Since the slower train is moving in the other direction though, it will take (350/ x+y) seconds to cross.
\(\frac{350}{(x + y)} = 10\)
\(\frac{35}{(x + y)} = 1\)
\(35 = x + y\) (Equation 2)
Solving these two equations, you get x = 20 m/s, and y = 15 m/s.
Let the faster train run at x m/s and the slower train run at y m/s.
The first statement states that it will take 70 seconds to cross each other running in the same direction. The first important thing her is that the faster train is behind the slower train, otherwise they would never cross. Secondly, in order to cross the slower train, the faster train will need to cover 350m MORE (250 m + 100 m) in the 70 seconds than the other train.
\(\frac{350}{(x - y)} = 70\)
\(\frac{5}{(x - y)} = 1\)
\(5 = x - y\) (Equation 1)
The second statement states that it will take 10 seconds to cross each other running in the opposite direction. The difference between this and running in the same direction, is that the slower train's speed CONTRIBUTES to the cross rather than inhibiting it. If the slower train was standing still, the faster train would take (350/x) seconds to pass it. Since the slower train is moving in the other direction though, it will take (350/ x+y) seconds to cross.
\(\frac{350}{(x + y)} = 10\)
\(\frac{35}{(x + y)} = 1\)
\(35 = x + y\) (Equation 2)
Solving these two equations, you get x = 20 m/s, and y = 15 m/s.
manojgmat
Two trains of length 100m and 250m run on parallel lines. when they run in the same direction it will take 70 sec to cross each other and when they run in opposite direction, they take 10 sec to cross each other. find the speed of faster train.
Alternative approach:
To cross each other (either in same or opposite direction), the trains have to cover a distance of 250 + 100 = 350 m (the faster train should cover the entire slower train and then its own length so that they completely cross each other)
When they run in the same direction, they cover this distance in 70 sec. So their relative speed in this case (which is the difference in their speeds) is 350/70 = 5 m/s
When they run in opposite directions, they cover this distance in 10 sec. So their relative speed in this case (which is the sum of their speeds) is 350/10 = 35 m/s
If sum if 35 and difference is 5, you should quickly jump to 20 and 15.
Note: We used the concept of relative speed here.
When 2 objects move in same direction, their relative speed i.e. speed relative to each other is the difference of their speeds.
When the 2 objects move in opposite directions, their relative speed i.e. speed relative to each other is the sum of their speeds.
Check this video for when to use relative speed: https://youtu.be/wrYxeZ2WsEM
