GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 17 Dec 2018, 11:15

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
  • 10 Keys to nail DS and CR questions

     December 17, 2018

     December 17, 2018

     06:00 PM PST

     07:00 PM PST

    Join our live webinar and learn how to approach Data Sufficiency and Critical Reasoning problems, how to identify the best way to solve each question and what most people do wrong.
  • R1 Admission Decisions: Estimated Decision Timelines and Chat Links for Major BSchools

     December 17, 2018

     December 17, 2018

     10:00 PM PST

     11:00 PM PST

    From Dec 5th onward, American programs will start releasing R1 decisions. Chat Rooms: We have also assigned chat rooms for every school so that applicants can stay in touch and exchange information/update during decision period.

A train crosses a bridge of length 500 m in 40 seconds and a lamp post

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51263
A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 01:27
2
14
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

63% (01:38) correct 37% (02:11) wrong based on 203 sessions

HideShow timer Statistics

A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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?
Extra-hard Quant Tests with Brilliant Analytics

Director
Director
avatar
P
Joined: 21 May 2013
Posts: 652
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 02:32
1
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.

Let Length of train=LT
Speed of train=VT

Time taken =(Length of train +Length of Bridge)/Speed of Train
40=(LT+500)VT
And, LT/VT=15
Put LT/VT=15 in the first equation,
15+500/VT=40
VT=20
Using value of VT=20, LT=300M
Answer E
Manager
Manager
avatar
Joined: 08 Sep 2012
Posts: 61
Location: India
Concentration: Social Entrepreneurship, General Management
WE: Engineering (Investment Banking)
GMAT ToolKit User Reviews Badge
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 03:19
1
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.



Length of train = L
Speed of train = S

(L+500) = S*40
L = S*15 => S = (L / 15)

=> L+500 = (L / 15) * 40
=> L = 300m

Option E
_________________

+1 Kudos if you liked my post! Thank you!

CEO
CEO
User avatar
P
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2711
Location: India
GMAT: INSIGHT
WE: Education (Education)
Reviews Badge
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 06:10
3
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


Let Length of Train = L

Case-1: Distance = 500+L (While crossing the bridge)
Time = 40 Seconds
i.e. Speed = Distance / Time = (500+L)/40

Case-2: Distance = L (While passing the lamp post)
Time = 15 Seconds
i.e. Speed = Distance / Time = (L)/15

But Since speed has to be same in both cases so

(500+L)/40 = (L)/15

i.e. 8L = 3L + 1500
i.e. 5L = 1500
i.e. L = 300

Answer: option E
_________________

Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION

Manager
Manager
User avatar
Joined: 10 Jun 2015
Posts: 118
A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 06:39
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


let the length of the train is L
L/15 = (L+500)/40
solving, L=300
Manager
Manager
User avatar
Joined: 14 Mar 2014
Posts: 146
GMAT 1: 710 Q50 V34
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 18 Aug 2015, 20:56
1
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


IMO: E

Speed = \(\frac{Distance}{time}\)

Let Length of train be \(L_T\)
Let Length of Bridge be \(L_B\)
Speed of train be S

While crossing Lamp post
S = \(\frac{L_T}{15}\)
\(L_T\) = 15S --(i)

While crossing Bridge
s = \(\frac{L_T + L_B}{40}\)
40s = \(L_T\)+\(L_B\)
40s = 15s+500 (from eq--(i) & given length of bridge = 500)
s= 20

Sub in eq-(i) we get \(L_T\) = 300
_________________

I'm happy, if I make math for you slightly clearer
And yes, I like kudos
¯\_(ツ)_/¯ :-)

Retired Moderator
avatar
Joined: 29 Apr 2015
Posts: 843
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
GMAT ToolKit User Premium Member
A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 21 Oct 2015, 10:36
1
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


You have two concepts covered in this topic: a train which crosses a stationary object with (1) and without (2) length:

Crossing a stationary object with length (bridge = 500m):

r * t = Length of Train + Length of object ->> Where r = spdeed and t = time

In this question we get: 40r = 500 + Length of Bridge

then crossing a stationary object without length/with negligible length:

r*t = Length of train

So we have 15r = Length of Train ->> plug in above to get:

40r = 500 + 15r
25r = 500
r = 20

Plug in r = 20 in 15r = Length of train to get Length = 300.
_________________

Saving was yesterday, heat up the gmatclub.forum's sentiment by spending KUDOS!

PS Please send me PM if I do not respond to your question within 24 hours.

Target Test Prep Representative
User avatar
P
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 4314
Location: United States (CA)
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 19 May 2017, 05:31
1
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m


We can let x = the length of the train in metres. To cross the 500-m bridge in 40 seconds, the head of the train must enter at one end of the bridge and the tail of the train must exit from the other end of the bridge. Therefore, in 40 seconds, the train actually travels the length of the bridge plus the train’s body length. In other words, the train travels (500 + x) metres in 40 seconds. If we let r be the speed of the train, we have:

500 + x = 40r

Since there are two unknowns, we need another equation in order to solve for x. We will use the fact that the train crosses a lamp post on the bridge in 15 seconds. This means that after the head of the train first crosses the lamp post, it takes 15 seconds for the train’s tail to cross the lamp post too. In other words, the train travels a distance equal to its body length in 15 seconds. So, we have:

x = 15r

Substitute x = 15r in the first equation and we have:

500 + 15r = 40r

500 = 25r

20 = r

So, we know the speed of the train is 20 m/s and its body length is x = 15r = 15(20) = 300 metres.

Answer: E
_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

VP
VP
User avatar
D
Joined: 09 Mar 2016
Posts: 1246
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 28 Oct 2018, 04:01
GMATinsight wrote:
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


Let Length of Train = L

Case-1: Distance = 500+L (While crossing the bridge)
Time = 40 Seconds
i.e. Speed = Distance / Time = (500+L)/40

Case-2: Distance = L (While passing the lamp post)
Time = 15 Seconds
i.e. Speed = Distance / Time = (L)/15

But Since speed has to be same in both cases so

(500+L)/40 = (L)/15

i.e. 8L = 3L + 1500
i.e. 5L = 1500
i.e. L = 300

Answer: option E


hey GMATinsight
not familiar with such type of questions. are there specific formulas for such concepts ? :)
thanks!
Manager
Manager
avatar
G
Joined: 14 Jun 2018
Posts: 222
CAT Tests
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 28 Oct 2018, 06:59
1
dave13 wrote:
GMATinsight wrote:
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


Let Length of Train = L

Case-1: Distance = 500+L (While crossing the bridge)
Time = 40 Seconds
i.e. Speed = Distance / Time = (500+L)/40

Case-2: Distance = L (While passing the lamp post)
Time = 15 Seconds
i.e. Speed = Distance / Time = (L)/15

But Since speed has to be same in both cases so

(500+L)/40 = (L)/15

i.e. 8L = 3L + 1500
i.e. 5L = 1500
i.e. L = 300

Answer: option E


hey GMATinsight
not familiar with such type of questions. are there specific formulas for such concepts ? :)
thanks!

hey , this should help with train related concepts https://www.hitbullseye.com/Quant/Probl ... Trains.php
e-GMAT Representative
User avatar
D
Joined: 04 Jan 2015
Posts: 2324
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 28 Oct 2018, 13:32

Solution



Given:
    • A train crosses a bridge of length 500 m in 40 seconds.
    • A train crosses a lamp post on the bridge in 15 seconds.

To find:
    • Length of the train in metres.

Approach and Working

Let the length of train is ‘t’ metres and speed of train is ‘s’ m/s.
    • Therefore, we can frame two equations.

A train crosses a bridge of length 500 m in 40 seconds.
    • In this case, train covers its length as well as the distance of bridge.
      o Hence, t+500= 40*s------(1)

A train crosses a lamp post on the bridge in 15 seconds.

    • In this case, train covers only its length.
      o Hence, t= 15*s

    • Substituting this value of t in equation 1, we get:
      o 15s +500 = 40s
      o 25s=500
      o s= 20 m/s
         Hence, t= 15*20= 300 m

Correct answer: Option E
_________________








Register for free sessions
Number Properties | Algebra |Quant Workshop

Success Stories
Guillermo's Success Story | Carrie's Success Story

Ace GMAT quant
Articles and Question to reach Q51 | Question of the week

Must Read Articles
Number Properties – Even Odd | LCM GCD | Statistics-1 | Statistics-2 | Remainders-1 | Remainders-2
Word Problems – Percentage 1 | Percentage 2 | Time and Work 1 | Time and Work 2 | Time, Speed and Distance 1 | Time, Speed and Distance 2
Advanced Topics- Permutation and Combination 1 | Permutation and Combination 2 | Permutation and Combination 3 | Probability
Geometry- Triangles 1 | Triangles 2 | Triangles 3 | Common Mistakes in Geometry
Algebra- Wavy line | Inequalities

Practice Questions
Number Properties 1 | Number Properties 2 | Algebra 1 | Geometry | Prime Numbers | Absolute value equations | Sets



| '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com

CEO
CEO
User avatar
P
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2711
Location: India
GMAT: INSIGHT
WE: Education (Education)
Reviews Badge
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 29 Oct 2018, 00:55
1
dave13 wrote:
GMATinsight wrote:
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


Let Length of Train = L

Case-1: Distance = 500+L (While crossing the bridge)
Time = 40 Seconds
i.e. Speed = Distance / Time = (500+L)/40

Case-2: Distance = L (While passing the lamp post)
Time = 15 Seconds
i.e. Speed = Distance / Time = (L)/15

But Since speed has to be same in both cases so

(500+L)/40 = (L)/15

i.e. 8L = 3L + 1500
i.e. 5L = 1500
i.e. L = 300

Answer: option E


hey GMATinsight
not familiar with such type of questions. are there specific formulas for such concepts ? :)
thanks!


dave13

Search for Time speed and distance questions and you would find plenty of such questions

There are not many formulas only a few concepts like Relative speed, River and boat problems etc.
_________________

Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION

Intern
Intern
avatar
B
Joined: 07 Jul 2018
Posts: 24
CAT Tests
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post  [#permalink]

Show Tags

New post 04 Nov 2018, 04:30
GMATinsight wrote:
Bunuel wrote:
A train crosses a bridge of length 500 m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?

A. 375 m
B. 750 m
C. 250 m
D. 800 m
E. 300 m

Kudos for a correct solution.


Let Length of Train = L

Case-1: Distance = 500+L (While crossing the bridge)
Time = 40 Seconds
i.e. Speed = Distance / Time = (500+L)/40

Case-2: Distance = L (While passing the lamp post)
Time = 15 Seconds
i.e. Speed = Distance / Time = (L)/15

But Since speed has to be same in both cases so

(500+L)/40 = (L)/15

i.e. 8L = 3L + 1500
i.e. 5L = 1500
i.e. L = 300

Answer: option E

I'm not able to understand the basic thing. Can you please explain why we add length of train and bridge length but in case of lamp post, why do we take train length? Shouldn't it be lamp post's length?
GMAT Club Bot
Re: A train crosses a bridge of length 500 m in 40 seconds and a lamp post &nbs [#permalink] 04 Nov 2018, 04:30
Display posts from previous: Sort by

A train crosses a bridge of length 500 m in 40 seconds and a lamp post

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.