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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

A man cycling along the road noticed that every 12 minutes [#permalink]

Show Tags

04 Jan 2010, 04:44

7

This post received KUDOS

113

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

95% (hard)

Question Stats:

38% (02:14) correct
62% (01:58) wrong based on 1021 sessions

HideShow timer Statistics

A man cycling along the road noticed that every 12 minutes a bus overtakes him and every 4 minutes he meets an oncoming bus. If all buses and the cyclist move at a constant speed, what is the time interval between consecutive buses?

A. 5 minutes B. 6 minutes C. 8 minutes D. 9 minutes E. 10 minutes

I didn't get how to solve this problem. Can someone explain me more detailed than solution provided by the test? Thank you in advance!!

A man cycling along the road noticed that every 12 minutes a bus overtakes him and every 4 minutes he meets an oncoming bus. If all buses and the cyclist move at a constant speed, what is the time interval between consecutive buses?

I didn't get how to solve this problem. Can someone explain me more detailed than solution provided by the test? Thank you in advance!!

A man cycling along the road noticed that every 12 minutes a bus overtakes him and every 4 minutes he meets an oncoming bus. If all buses and the cyclist move at a constant speed, what is the time interval between consecutive buses? A. 5 minutes B. 6 minutes C. 8 minutes D. 9 minutes E. 10 minutes

Let's say the distance between the buses is \(d\). We want to determine \(Interval=\frac{d}{b}\), where \(b\) is the speed of bus.

Let the speed of cyclist be \(c\).

Every 12 minutes a bus overtakes cyclist: \(\frac{d}{b-c}=12\), \(d=12b-12c\);

Every 4 minutes cyclist meets an oncoming bus: \(\frac{d}{b+c}=4\), \(d=4b+4c\);

I might be VERY wrong..But when i don't get the answers..I go off track..So I'm not sure that this is the answer.. But marking the answer with some guess is better than NO guess.!!

Let say the road is a straight line AB. The cyclist starts frm A and Bus starts frm B.

So in 4 min, let the distance traveled by Cyc is x, so distance traveled by Bus is (AB - x) so 4 = x/c...........................1 and 4= (AB - x)/b..................................2 where c and b are respective speed of the cyclist and bus

Also in 12 mins, distance traveled by cyc is 3x.

so 12= 3x/(b-c) and x= 4c (frm 1) so 1= c/(b-c) and b=2c........................3

put the value of b frm 3 in equation 2.

We get AB=12c

So now the total distance is 12c and bus speed is 2c. The bus travels in 6 min...

It's A COMPLETE WILD GUESS..!! I was not able to get answer in 2 min..Let me knw the OA and OE.

Let's say the distance between the buses is \(d\). We want to determine \(Interval=\frac{d}{b}\), where \(b\) is the speed of bus. Let the speed of cyclist be \(c\).

\(Interval=\frac{d}{b}=\frac{6b}{b}=6\)

Answer: 6 minutes.

Hope it helps.

Thanks for the explanation. Please clarify the following doubts. Aren't we calculating the interval between 2 buses that move towards each other? If yes, then would the interval not be 6b/b+b ?

Let's say the distance between the buses is \(d\). We want to determine \(Interval=\frac{d}{b}\), where \(b\) is the speed of bus. Let the speed of cyclist be \(c\).

\(Interval=\frac{d}{b}=\frac{6b}{b}=6\)

Answer: 6 minutes.

Hope it helps.

Thanks for the explanation. Please clarify the following doubts. Aren't we calculating the interval between 2 buses that move towards each other? If yes, then would the interval not be 6b/b+b ?

Not sure I understood your question...

Anyway: question asks "what is the time interval between consecutive buses". Or time intervals between subsequent bus arrivals to a given bus stop (some static point). Which is: constant distance between two subsequent buses divided by the constant rate of these buses d/b. After some calculations we've gotten that d=6b, hence d/b=6b/b=6.
_________________

Let's say the distance between the buses is \(d\). We want to determine \(Interval=\frac{d}{b}\), where \(b\) is the speed of bus. Let the speed of cyclist be \(c\).

\(Interval=\frac{d}{b}=\frac{6b}{b}=6\)

Answer: 6 minutes.

Hope it helps.

Thanks for the explanation. Please clarify the following doubts. Aren't we calculating the interval between 2 buses that move towards each other? If yes, then would the interval not be 6b/b+b ?

Not sure I understood your question...

Anyway: question asks "what is the time interval between consecutive buses". Or time intervals between subsequent bus arrivals to a given bus stop (some static point). Which is: constant distance between two subsequent buses divided by the constant rate of these buses d/b. After some calculations we've gotten that d=6b, hence d/b=6b/b=6.

Thanks bunnel for the explanation. But I have a doubt here. what is the time interval between consecutive buses? Isn't it the time interval between consecutive buses going in one direction. If that is the case then ans should be 12 min. Thanks.
_________________

Thanks bunnel for the explanation. But I have a doubt here. what is the time interval between consecutive buses? Isn't it the time interval between consecutive buses going in one direction. If that is the case then ans should be 12 min. Thanks.

yeah if you standing at a busstop then whats the time interval of arrival of bus.--> you may take the question this way.

use relative velocity:

vel of bus=a vel of cyclist=b distance between them=d

now, d=12(a-b)=4(a+b)

hence d=6a so time interval is d/a=6 min

hope this clarifies...!!
_________________

Practice Practice and practice...!!

If my reply /analysis is helpful-->please press KUDOS If there's a loophole in my analysis--> suggest measures to make it airtight.

Thanks bunnel for the explanation. But I have a doubt here. what is the time interval between consecutive buses? Isn't it the time interval between consecutive buses going in one direction. If that is the case then ans should be 12 min. Thanks.

yeah if you standing at a busstop then whats the time interval of arrival of bus.--> you may take the question this way.

use relative velocity:

vel of bus=a vel of cyclist=b distance between them=d

now, d=12(a-b)=4(a+b)

hence d=6a so time interval is d/a=6 min

hope this clarifies...!!

Thanks kraizada84 for explanation, but still yeah if you standing at a busstop then whats the time interval of arrival of bus.--> you may take the question this way. not making sense to me. If you are standing at a bus stop then the interval of arrival of bus will be in one direction only. But here we are calculating for both direction.

You see in ONE DIRECTION, the distance between two buses is "d", the speed of the buses is "b"(lets just say its km/minute). So to find this interval, we take this distance divided by speed of bus(all in ONE DIRECTION). so d/b.

Now through algebra 12(a-b)=4(a+b) , we find that distance "d" is equal to "6b". remember d is distance between two buses in ONE DIRECTION. And so we do the division and get the answer 6 minutes.

Just because we do this algebra equation d=12(a-b)=4(a+b), doesn't mean that the nature of b,c or d has changed. It stays true to its original meaning.

No idea what else can clear up your confusion :S
_________________

Question Bank Extracted from the GMATPrep Software: 857 Verbal Questions: http://gmatclub.com/forum/gmatprep-verbal-question-bank-130070.html 393 Quant PS Questions: http://gmatclub.com/forum/gmatprep-ps-question-bank-130073.html 436 Quant DS Questions: http://gmatclub.com/forum/gmatprep-ds-question-bank-130069.html

Thanks for the explanation. Please clarify the following doubts. Aren't we calculating the interval between 2 buses that move towards each other? If yes, then would the interval not be 6b/b+b ?

Not sure I understood your question...

Anyway: question asks "what is the time interval between consecutive buses". Or time intervals between subsequent bus arrivals to a given bus stop (some static point). Which is: constant distance between two subsequent buses divided by the constant rate of these buses d/b. After some calculations we've gotten that d=6b, hence d/b=6b/b=6.

Thanks bunnel for the explanation. But I have a doubt here. what is the time interval between consecutive buses? Isn't it the time interval between consecutive buses going in one direction. If that is the case then ans should be 12 min. Thanks.

Consecutive buses mean consecutive buses in one direction, how else? So, if the distance between two consecutive buses is \(d\) and the rate of the bus is \(b\) then \(Interval=\frac{d}{b}\).

Re: A man cycling along the road noticed that every 12 minutes [#permalink]

Show Tags

30 Apr 2012, 13:28

Hi Bunuel,

This is regarding the solution you gave:

Let's say the distance between the buses is d. We want to determine Interval=\frac{d}{b}, where b is the speed of bus.

Let the speed of cyclist be c.

Every 12 minutes a bus overtakes cyclist: \frac{d}{b-c}=12, d=12b-12c;

Every 4 minutes cyclist meets an oncoming bus: \frac{d}{b+c}=4, d=4b+4c;

d=12b-12c=4b+4c, --> b=2c, --> d=12b-6b=6b.

Interval=\frac{d}{b}=\frac{6b}{b}=6

Answer: B (6 minutes).

when you say distance between 2 buses is d, you mean to buses that start at opposite ends right? ex. after 12 mins (POINT A)starting point for busA --------------cyclist(busA meets him here)-----------------staring point for busB -------------------------distance d -----------------------

then how is following possible coz d is the total distance not the distance between busA staring point and meeting point with cyclist. Every 12 minutes a bus overtakes cyclist: \frac{d}{b-c}=12, d=12b-12c;

Plus, is the question asking for interval between when 2 buses leave staring point of busA(POINT A)?

Let's say the distance between the buses is d. We want to determine Interval=\frac{d}{b}, where b is the speed of bus.

Let the speed of cyclist be c.

Every 12 minutes a bus overtakes cyclist: \frac{d}{b-c}=12, d=12b-12c;

Every 4 minutes cyclist meets an oncoming bus: \frac{d}{b+c}=4, d=4b+4c;

d=12b-12c=4b+4c, --> b=2c, --> d=12b-6b=6b.

Interval=\frac{d}{b}=\frac{6b}{b}=6

Answer: B (6 minutes).

when you say distance between 2 buses is d, you mean to buses that start at opposite ends right? ex. after 12 mins (POINT A)starting point for busA --------------cyclist(busA meets him here)-----------------staring point for busB -------------------------distance d -----------------------

then how is following possible coz d is the total distance not the distance between busA staring point and meeting point with cyclist. Every 12 minutes a bus overtakes cyclist: \frac{d}{b-c}=12, d=12b-12c;

Plus, is the question asking for interval between when 2 buses leave staring point of busA(POINT A)?

thanks,

No, the distance between the buses is \(d\) means that \(d\) is the distance between two subsequent buses.
_________________

Re: A man cycling along the road noticed that every 12 minutes [#permalink]

Show Tags

02 May 2012, 23:02

Can I assume that since Cyclist is meeting an oncoming bus every 4 minutes, his speed is 4km/hr? or lets assume that a bus crosses him every 12 minutes coming from back and in 4 minutes coming from front. Thus cumulative speed is 16km/hr however cyclist himself is also moving forward @4km/hr. Thus net effect is 12km/hr. Beyond that, I am confused.

Can I assume that since Cyclist is meeting an oncoming bus every 4 minutes, his speed is 4km/hr? or lets assume that a bus crosses him every 12 minutes coming from back and in 4 minutes coming from front. Thus cumulative speed is 16km/hr however cyclist himself is also moving forward @4km/hr. Thus net effect is 12km/hr. Beyond that, I am confused.

No you can not assume that. Please refer to the solutions given above.
_________________

Can I assume that since Cyclist is meeting an oncoming bus every 4 minutes, his speed is 4km/hr? or lets assume that a bus crosses him every 12 minutes coming from back and in 4 minutes coming from front. Thus cumulative speed is 16km/hr however cyclist himself is also moving forward @4km/hr. Thus net effect is 12km/hr. Beyond that, I am confused.

I am not sure how you are assuming speeds, but if you are looking for a relatively theoretical solution, you can think in this way:

Say the cyclist is stationary at a point. Buses are coming from opposite directions (same speed, same time interval). A bus will meet the cyclist every t minutes from either direction. Let's say, a bus from each direction just met him. After t minutes, 2 more buses from opposite directions will meet him again and so on...

Now if the cyclist starts moving, (cyclist speed = c and bus speed = b), the ratio of the relative speeds of the buses is the inverse of the ratio of time taken i.e. it will be 4:12

(b-c):(b+c) = 4:12 which gives you c = (1/2)b

This means that the bus travelling at a relative speed which is half its usual speed (b-c = b/2) takes 12 minutes to meet the man. If it were travelling at its usual speed, it would have taken 12/2 = 6 mins to meet the man.
_________________

why is the distance between buses a constant value?

Assume that starting from a bus station, all buses run at the same speed of 50 mph. Say a bus starts at 12:00 noon. Another starts at 1:00 pm i.e. exactly one hr later on the same route. Can we say that the previous bus is 50 miles away at 1:00 pm? Yes, so the distance between the two buses initially will be 50 miles. The 1 o clock bus also runs at 50 mph. Will the distance between these two buses always stay the same i.e. the initial 50 miles? Since both buses are moving at the same speed of 50 mph, relative to each other, they are not moving at all and the distance between them remains constant.

The exact same concept is used in this question.
_________________

A man cycling along the road noticed that every 12 minutes a bus overtakes him and every 4 minutes he meets an oncoming bus. If all buses and the cyclist move at a constant speed, what is the time interval between consecutive buses?

I didn't get how to solve this problem. Can someone explain me more detailed than solution provided by the test? Thank you in advance!!

A man cycling along the road noticed that every 12 minutes a bus overtakes him and every 4 minutes he meets an oncoming bus. If all buses and the cyclist move at a constant speed, what is the time interval between consecutive buses? A. 5 minutes B. 6 minutes C. 8 minutes D. 9 minutes E. 10 minutes

Let's say the distance between the buses is \(d\). We want to determine \(Interval=\frac{d}{b}\), where \(b\) is the speed of bus.

Let the speed of cyclist be \(c\).

Every 12 minutes a bus overtakes cyclist: \(\frac{d}{b-c}=12\), \(d=12b-12c\);

Every 4 minutes cyclist meets an oncoming bus: \(\frac{d}{b+c}=4\), \(d=4b+4c\);