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

It is currently 19 Sep 2014, 13:57

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

A train always travels at one of two speeds: 160 km/hr in

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
GMAT Instructor
avatar
Joined: 04 Jul 2006
Posts: 1270
Location: Madrid
Followers: 23

Kudos [?]: 125 [0], given: 0

A train always travels at one of two speeds: 160 km/hr in [#permalink] New post 09 Dec 2007, 06:27
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 1 sessions
A train always travels at one of two speeds: 160 km/hr in rural areas and 40 km/hr in urban areas. Was its average speed from A to B greater than 100 km/hr?

(1) More than 2/3 of the distance from A to B is through rural areas.
(2) The distance from A to B is more than 1000 km.
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3571
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 364

Kudos [?]: 1794 [0], given: 358

GMAT ToolKit User GMAT Tests User Premium Member
 [#permalink] New post 09 Dec 2007, 06:56
Expert's post
A.

(1) V=(Lu+Lr)/(Lu/40+Lr/160), let k=Lr/Lu=(2/3)/(1/3)=2 ==>
V=(1+2)/(1/40+2/160)=3*160/(4+2)=80 km/h - suff

(2) The distance from A to B does not influence on average speed.- insuff
Director
Director
avatar
Joined: 09 Jul 2005
Posts: 595
Followers: 2

Kudos [?]: 21 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 08:19
The more the train travels through rural a areas, the greater its average speed. Lets calculate the relationship between Lu and Lr so that the average speed is 100 km/h

v=[Lu+Lr]/[Lu/40 + Lr/160]=100 => Lr/Lu=4 which means that in order to reach an average speed of 100 km/h, the train must travel 1/5 of the distance through urban areas and 4/5 of the distance through rural areas. So in order to reach an average speed greater than 100 km/h, the train must travel less than 1/5 of the distance through urban areas and more than 4/5 of the distance through rural areas.

Therefore, we can not conclude anything from S1 nor S2

OA should be E
Director
Director
User avatar
Joined: 12 Jul 2007
Posts: 867
Followers: 12

Kudos [?]: 199 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 08:38
kevincan wrote:
A train always travels at one of two speeds: 160 km/hr in rural areas and 40 km/hr in urban areas. Was its average speed from A to B greater than 100 km/hr?

(1) More than 2/3 of the distance from A to B is through rural areas.
(2) The distance from A to B is more than 1000 km.


1. Since the distance doesn't matter, let's plug in 480km for the distance and say that exactly 2/3 of the distance from A to B is rural (since we don't know exactly how much it is)
320km = rural
160km = urban

320km/160 = 2 hours in rural
160km/40 = 4 hours in urban
480km/6 hours = 80km/h

INSUFFICIENT

2. distance doesn't matter. INSUFFICIENT

Answer E

this is a great example of the test makers favorite trick with averages. It's the TIME spent at each speed that we need to get the average, NOT the distance.
CEO
CEO
User avatar
Joined: 29 Mar 2007
Posts: 2593
Followers: 16

Kudos [?]: 189 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:04
automan wrote:
The more the train travels through rural a areas, the greater its average speed. Lets calculate the relationship between Lu and Lr so that the average speed is 100 km/h

v=[Lu+Lr]/[Lu/40 + Lr/160]=100 => Lr/Lu=4 which means that in order to reach an average speed of 100 km/h, the train must travel 1/5 of the distance through urban areas and 4/5 of the distance through rural areas. So in order to reach an average speed greater than 100 km/h, the train must travel less than 1/5 of the distance through urban areas and more than 4/5 of the distance through rural areas.

Therefore, we can not conclude anything from S1 nor S2

OA should be E


I'm not convinced the answer is E. It seems we can conclude something from A. In your analysis you said that in order to have an avg. speed greater than 100km/hr the train needs to travel 4/5 the distance at 160km/hr.

Well S1 tells us that it will travel exactly 2/3 of the distance at 160km/hr. So we can answer a definitive NO for s1. The train will not exceed 100km/hr. S2 is irrelevant.

Knowing the ratio here is enough.

1. Since the distance doesn't matter, let's plug in 480km for the distance and say that exactly 2/3 of the distance from A to B is rural (since we don't know exactly how much it is)
320km = rural
160km = urban

320km/160 = 2 hours in rural
160km/40 = 4 hours in urban
480km/6 hours = 80km/h

You found the answer here... 80km/hr... We know that the train will NEVER exceed 100km/hr b/c the ratio is 2/3.

I was w/ A and im still w/ A/
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3571
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 364

Kudos [?]: 1794 [0], given: 358

GMAT ToolKit User GMAT Tests User Premium Member
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:22
Expert's post
I think Eschn3am is right.

(1) More than 2/3 of the distance from A to B is through rural areas.

therefore, 80<Vavr<=160. insuff.

+1 Kudos :)
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

CEO
CEO
User avatar
Joined: 29 Mar 2007
Posts: 2593
Followers: 16

Kudos [?]: 189 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:26
walker wrote:
I think Eschn3am is right.

(1) More than 2/3 of the distance from A to B is through rural areas.

therefore, 80<Vavr<=160. insuff.

+1 Kudos :)


Ah MAN.... lol I hate it when that happens. def. Kudos to Eschn3am.
Director
Director
avatar
Joined: 09 Jul 2005
Posts: 595
Followers: 2

Kudos [?]: 21 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:36
GMATBLACKBELT wrote:
automan wrote:
The more the train travels through rural a areas, the greater its average speed. Lets calculate the relationship between Lu and Lr so that the average speed is 100 km/h

v=[Lu+Lr]/[Lu/40 + Lr/160]=100 => Lr/Lu=4 which means that in order to reach an average speed of 100 km/h, the train must travel 1/5 of the distance through urban areas and 4/5 of the distance through rural areas. So in order to reach an average speed greater than 100 km/h, the train must travel less than 1/5 of the distance through urban areas and more than 4/5 of the distance through rural areas.

Therefore, we can not conclude anything from S1 nor S2

OA should be E


I'm not convinced the answer is E. It seems we can conclude something from A. In your analysis you said that in order to have an avg. speed greater than 100km/hr the train needs to travel 4/5 the distance at 160km/hr.

Well S1 tells us that it will travel exactly 2/3 of the distance at 160km/hr. So we can answer a definitive NO for s1. The train will not exceed 100km/hr. S2 is irrelevant.

Knowing the ratio here is enough.

1. Since the distance doesn't matter, let's plug in 480km for the distance and say that exactly 2/3 of the distance from A to B is rural (since we don't know exactly how much it is)
320km = rural
160km = urban

320km/160 = 2 hours in rural
160km/40 = 4 hours in urban
480km/6 hours = 80km/h

You found the answer here... 80km/hr... We know that the train will NEVER exceed 100km/hr b/c the ratio is 2/3.

I was w/ A and im still w/ A/


You have calculated that if the train travels 2/3 of the distance through rural areas the average speed is 80 km/h . Now imagine that the train travels all the time through rural areas, making S1 true (the train travel 100% of the time through rural areas). In this case the average speed is 160 km/h. Therefore we can no conclude anything.

I hope this makes my reasoning more understable.
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3571
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 364

Kudos [?]: 1794 [0], given: 358

GMAT ToolKit User GMAT Tests User Premium Member
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:38
Expert's post
automan, +1 Kudos :)
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Director
Director
avatar
Joined: 09 Jul 2005
Posts: 595
Followers: 2

Kudos [?]: 21 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:42
walker wrote:
automan, +1 Kudos :)


Another one for you. You always try the most difficult questions!! I have a lot to learn from you
Manager
Manager
User avatar
Joined: 01 Jan 2008
Posts: 227
Schools: Booth, Stern, Haas
Followers: 1

Kudos [?]: 44 [0], given: 2

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:46
walker wrote:
I think Eschn3am is right.

(1) More than 2/3 of the distance from A to B is through rural areas.

therefore, 80<Vavr<=160. insuff.

+1 Kudos :)



why it is insufficient? I agree 80<Vavr but still you have information to solve problem,
am I missing some point? :|
Director
Director
User avatar
Joined: 12 Jul 2007
Posts: 867
Followers: 12

Kudos [?]: 199 [0], given: 0

GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:48
kazakhb wrote:
walker wrote:
I think Eschn3am is right.

(1) More than 2/3 of the distance from A to B is through rural areas.

therefore, 80<Vavr<=160. insuff.

+1 Kudos :)



why it is insufficient? I agree 80<Vavr but still you have information to solve problem,
am I missing some point? :|


We want to know if the average speed is greater than 100km/h. Given the information from statement one we see that the average speed must be greater than 80km/h and less than or equal to 160km/h.

80 < average <= 160

this isn't enough to know if the average is greater than 100 because it could be 81 or 160.

and statement 2 doesn't help us at all because the averages will work out to be the same, regardless of distance.
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3571
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 364

Kudos [?]: 1794 [0], given: 358

GMAT ToolKit User GMAT Tests User Premium Member
Re: DS: Train [#permalink] New post 06 Jan 2008, 09:50
Expert's post
kazakhb wrote:
walker wrote:
I think Eschn3am is right.

(1) More than 2/3 of the distance from A to B is through rural areas.

therefore, 80<Vavr<=160. insuff.

+1 Kudos :)



why it is insufficient? I agree 80<Vavr but still you have information to solve problem,
am I missing some point? :|


Q. Was its average speed from A to B greater than 100 km/hr?
1. 80<Vavr<=160, So, speed greater 100? maybe yes and maybe no
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Senior Manager
Senior Manager
User avatar
Joined: 19 Nov 2007
Posts: 477
Followers: 3

Kudos [?]: 51 [0], given: 4

GMAT ToolKit User GMAT Tests User
Re: DS: Train [#permalink] New post 06 Jan 2008, 10:04
automan wrote:
GMATBLACKBELT wrote:
automan wrote:
The more the train travels through rural a areas, the greater its average speed. Lets calculate the relationship between Lu and Lr so that the average speed is 100 km/h

v=[Lu+Lr]/[Lu/40 + Lr/160]=100 => Lr/Lu=4 which means that in order to reach an average speed of 100 km/h, the train must travel 1/5 of the distance through urban areas and 4/5 of the distance through rural areas. So in order to reach an average speed greater than 100 km/h, the train must travel less than 1/5 of the distance through urban areas and more than 4/5 of the distance through rural areas.

Therefore, we can not conclude anything from S1 nor S2

OA should be E


I'm not convinced the answer is E. It seems we can conclude something from A. In your analysis you said that in order to have an avg. speed greater than 100km/hr the train needs to travel 4/5 the distance at 160km/hr.

Well S1 tells us that it will travel exactly 2/3 of the distance at 160km/hr. So we can answer a definitive NO for s1. The train will not exceed 100km/hr. S2 is irrelevant.

Knowing the ratio here is enough.

1. Since the distance doesn't matter, let's plug in 480km for the distance and say that exactly 2/3 of the distance from A to B is rural (since we don't know exactly how much it is)
320km = rural
160km = urban

320km/160 = 2 hours in rural
160km/40 = 4 hours in urban
480km/6 hours = 80km/h

You found the answer here... 80km/hr... We know that the train will NEVER exceed 100km/hr b/c the ratio is 2/3.

I was w/ A and im still w/ A/


You have calculated that if the train travels 2/3 of the distance through rural areas the average speed is 80 km/h . Now imagine that the train travels all the time through rural areas, making S1 true (the train travel 100% of the time through rural areas). In this case the average speed is 160 km/h. Therefore we can no conclude anything.

I hope this makes my reasoning more understable.



yes that reasoning seems far fetched, but one can't deny it.

Whats the OA kevin?
_________________

-Underline your question. It takes only a few seconds!
-Search before you post.

Manager
Manager
User avatar
Joined: 01 Jan 2008
Posts: 227
Schools: Booth, Stern, Haas
Followers: 1

Kudos [?]: 44 [0], given: 2

GMAT Tests User
Re: DS: Train [#permalink] New post 27 Nov 2008, 04:01
automan wrote:
The more the train travels through rural a areas, the greater its average speed. Lets calculate the relationship between Lu and Lr so that the average speed is 100 km/h

v=[Lu+Lr]/[Lu/40 + Lr/160]=100 => Lr/Lu=4 which means that in order to reach an average speed of 100 km/h, the train must travel 1/5 of the distance through urban areas and 4/5 of the distance through rural areas. So in order to reach an average speed greater than 100 km/h, the train must travel less than 1/5 of the distance through urban areas and more than 4/5 of the distance through rural areas.

Therefore, we can not conclude anything from S1 nor S2

OA should be E

can someone describe step by step how it can be simplified?
Re: DS: Train   [#permalink] 27 Nov 2008, 04:01
    Similar topics Author Replies Last post
Similar
Topics:
1 If a car moving at the speed of x km/hr travels a distance SravnaTestPrep 3 29 Jun 2013, 20:27
4 Experts publish their posts in the topic An express train traveled at an average speed of 100 ashkrs 6 25 Nov 2007, 20:00
A train always travels at one of two speeds: 160 km/hr in kevincan 19 08 Oct 2007, 10:55
At what speed was a train travelling on a trip when it had doloris 4 03 Jun 2005, 11:27
A train travels at an average speed of 90 km/hr without any krisrini 6 27 Apr 2005, 22:53
Display posts from previous: Sort by

A train always travels at one of two speeds: 160 km/hr in

  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®.