Find all School-related info fast with the new School-Specific MBA Forum

It is currently 23 Jul 2014, 00:22

Close

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

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Two trains of length 100m and 250m run on parallel lines

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
2 KUDOS received
Manager
Manager
avatar
Joined: 14 Dec 2008
Posts: 171
Followers: 1

Kudos [?]: 14 [2] , given: 39

GMAT Tests User
Two trains of length 100m and 250m run on parallel lines [#permalink] New post 29 Sep 2009, 10:55
2
This post received
KUDOS
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

56% (02:41) correct 44% (01:24) wrong based on 6 sessions
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.
6 KUDOS received
Manager
Manager
avatar
Joined: 11 Sep 2009
Posts: 129
Followers: 4

Kudos [?]: 159 [6] , given: 6

GMAT Tests User
Re: PS - Trains speed distance [#permalink] New post 29 Sep 2009, 12:01
6
This post received
KUDOS
1
This post was
BOOKMARKED
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.
Senior Manager
Senior Manager
avatar
Joined: 31 Aug 2009
Posts: 422
Location: Sydney, Australia
Followers: 6

Kudos [?]: 99 [0], given: 20

GMAT Tests User
Re: PS - Trains speed distance [#permalink] New post 30 Sep 2009, 05:01
AKprodigy87 - Nice clear response. Kudos
Manager
Manager
avatar
Joined: 14 Dec 2008
Posts: 171
Followers: 1

Kudos [?]: 14 [0], given: 39

GMAT Tests User
Re: PS - Trains speed distance [#permalink] New post 30 Sep 2009, 09:04
OA is 20m/s and 15m/s
Current Student
User avatar
Status: mba here i come!
Joined: 07 Aug 2011
Posts: 270
Location: Pakistan
Concentration: Strategy, Marketing
Schools: Insead '13 (M)
GMAT 1: 680 Q46 V37
GMAT 2: Q V
Followers: 23

Kudos [?]: 682 [0], given: 48

GMAT ToolKit User
Re: PS - Trains speed distance [#permalink] New post 13 Mar 2012, 05:44
relative speeds: \frac{350}{70}=5 and \frac{350}{10}=35

a+b=35, a-b=5

20m/s and 15m/s

_________________

press +1 Kudos to appreciate posts
Download Valuable Collection of Percentage Questions (PS/DS)

Intern
Intern
avatar
Joined: 03 Dec 2010
Posts: 22
Followers: 0

Kudos [?]: 2 [0], given: 0

Re: Two trains of length 100m and 250m run on parallel lines [#permalink] New post 28 Mar 2012, 21:58
Hello,

Though the explanation to the given problem is simple, could someone explain with example, as I still find it difficult to intrepret, which train is 100m and which one is 250 m long?

Thnx in advance.
Expert Post
3 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4566
Location: Pune, India
Followers: 1029

Kudos [?]: 4454 [3] , given: 162

Re: Two trains of length 100m and 250m run on parallel lines [#permalink] New post 29 Mar 2012, 00:03
3
This post received
KUDOS
Expert's post
manojgmat wrote:
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.

_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18684
Followers: 3232

Kudos [?]: 22231 [0], given: 2601

Re: Two trains of length 100m and 250m run on parallel lines [#permalink] New post 29 Mar 2012, 00:47
Expert's post
priyalr wrote:
Hello,

Though the explanation to the given problem is simple, could someone explain with example, as I still find it difficult to intrepret, which train is 100m and which one is 250 m long?

Thnx in advance.


We can not deduce whether 100m train or 250m train is faster, we just know that the rate of a faster train, whichever it is, is 20 m/s and and the rate of a slower train is 15 m/s.

So, as you can see we can answer the question even not knowing whether 100m train or 250m train is faster. Refer to ANY solution above (they are basically all the same) to see how it can be done.

Hope it helps.

_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

SVP
SVP
User avatar
Joined: 09 Sep 2013
Posts: 1708
Followers: 162

Kudos [?]: 33 [0], given: 0

Premium Member
Re: Two trains of length 100m and 250m run on parallel lines [#permalink] New post 15 Oct 2013, 18:37
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.

_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

SVP
SVP
User avatar
Joined: 06 Sep 2013
Posts: 1629
Location: United States
Concentration: Finance
GMAT 1: 710 Q48 V39
WE: Corporate Finance (Investment Banking)
Followers: 10

Kudos [?]: 132 [0], given: 254

GMAT ToolKit User
Re: Two trains of length 100m and 250m run on parallel lines [#permalink] New post 31 Dec 2013, 05:41
manojgmat wrote:
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.


We have

(a-b)(70) = (a+b)(10)

3a = 4b

We also know that (a-b)(70) = 350m
a-b =5

So a=20, b=15

The speed of the faster train is 20m/sec

Hope it helps
Cheers!
J :)
Re: Two trains of length 100m and 250m run on parallel lines   [#permalink] 31 Dec 2013, 05:41
    Similar topics Author Replies Last post
Similar
Topics:
4 Experts publish their posts in the topic Two trains 1& 2 start simultaneously and run on parallel innocous 1 23 Nov 2013, 03:57
13 Experts publish their posts in the topic Given line L, and a parallel line that runs through point 12bhang 7 13 Apr 2013, 04:16
5 Experts publish their posts in the topic Two trains run in opposite directions on a circular track. alex1233 14 15 May 2012, 12:47
1 Experts publish their posts in the topic Two trains, Q and P, are traveling on straight and parallel shekar123 4 23 May 2010, 08:24
Two lines are parallel to each other and other two lines pb_india 1 02 May 2005, 09:54
Display posts from previous: Sort by

Two trains of length 100m and 250m run on parallel lines

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.