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

 It is currently 26 May 2016, 22:09

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Mark biked from his house to his friend's house in how many

Author Message
TAGS:

### Hide Tags

Intern
Joined: 29 Dec 2011
Posts: 38
Followers: 0

Kudos [?]: 37 [0], given: 29

Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

25 Oct 2012, 20:44
1
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

67% (01:00) correct 33% (00:59) wrong based on 243 sessions

### HideShow timer Statistics

Mark biked from his house to his friend's house in how many hours?

(1) Mark bikes at an average speed of 72 blocks per hour.

(2) If Mark could bike an extra 8 blocks for each hour, he would have arrived at his friend's place 1 hour earlier

I got the correct answer (no spoilers!) but if I were to sit down and calculate the answer, how would I do it (I know purpose is not to calculate in DS, but it's really for practice, if anything).

Thanks again.
[Reveal] Spoiler: OA

Last edited by Bunuel on 26 Oct 2012, 04:26, edited 1 time in total.
Renamed the topic and edited the question.
Senior Manager
Joined: 11 May 2011
Posts: 373
Location: US
Followers: 3

Kudos [?]: 82 [0], given: 46

### Show Tags

25 Oct 2012, 21:17
elegan wrote:
Hello,

I'm looking at this question.

Mark biked from his house to his friend's house in how many hours?

1. Mark bikes at an average speed of 72 blocks per hour.

2. If Mark could bike an extra 8 blocks for each hour, he would have arrived at his friend's place 1 hour earlier

I got the correct answer (no spoilers!) but if I were to sit down and calculate the answer, how would I do it (I know purpose is not to calculate in DS, but it's really for practice, if anything).

Thanks again.

Mark bikes at an average speed of 72 blocks per hour.
Mark could bike an extra 8 blocks for each hour = 80 blocks per hour

LCM of 72 & 80 = 720. Time taken by Mark = 720/72 = 10 hrs.

Cheers!
_________________

-----------------------------------------------------------------------------------------
What you do TODAY is important because you're exchanging a day of your life for it!
-----------------------------------------------------------------------------------------

Manager
Joined: 29 Jul 2012
Posts: 189
GMAT Date: 11-18-2012
Followers: 0

Kudos [?]: 61 [0], given: 23

### Show Tags

25 Oct 2012, 23:15
why you took LCM?
to get a distance
can you explain in detial
_________________

Thriving for CHANGE

Director
Status: Done with formalities.. and back..
Joined: 15 Sep 2012
Posts: 647
Location: India
Concentration: Strategy, General Management
Schools: Olin - Wash U - Class of 2015
WE: Information Technology (Computer Software)
Followers: 43

Kudos [?]: 476 [0], given: 23

### Show Tags

25 Oct 2012, 23:41
Aristocrat wrote:
why you took LCM?
to get a distance
can you explain in detial

There is no sense in taking LCM in such problems. if question said he saved 2 hrs riding his bike 15 blocks/hr faster, the solution would go haywire.

to solve such problems:

Let d be the distance and t the time taken in first case. thus t-1 is time taken in second case.

therefore from 1:
$$t = d/72$$
and from 2:
$$t-1 = d/80$$

combining these:
$$t-1 = 72t /80$$
=>$$80t -80 =72t$$
=>$$t= 10 hrs$$

Hope it helps.
_________________

Lets Kudos!!!
Black Friday Debrief

Intern
Joined: 27 Sep 2012
Posts: 1
Followers: 0

Kudos [?]: 1 [1] , given: 2

### Show Tags

26 Oct 2012, 01:01
1
KUDOS
Another way of approaching this problem -

In all cases, if the speed increases by 1/x, the time taken decreases by 1/x+1 (as speed and time taken are inversely proportional to each other).

In this case the increase in speed is 1/9 (Mark's new speed is 72+8=80 blocks per hour, and the increase of 8 blocks per hour is 1/9th of his previous speed).

Therefore the corresponding decrease in time = 1/9+1 = 1/10. This represents 1/10th of the actual time taken.

1/10th of the actual time taken is given as 1 hour. Hence the total time taken is 10 hours.

Hope it helps.

Cheers!
Senior Manager
Joined: 13 May 2013
Posts: 472
Followers: 2

Kudos [?]: 130 [0], given: 134

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

01 Aug 2013, 13:08
Mark biked from his house to his friend's house in how many hours?

Time = Distance/Speed

(1) Mark bikes at an average speed of 72 blocks per hour.
There is no information given about the distance Mark has to travel. All we know is that r=72
INSUFFICIENT

(2) If Mark could bike an extra 8 blocks for each hour, he would have arrived at his friend's place 1 hour earlier
t-1 = d/(r+8)
We can try and plug in various other distance/time/rate formulas to try and cancel out variables but it's unlikely that will leave us with only one given that there are three variables to plug in for.
INSUFFICIENT

1+2) r=72 and t-1 = d/(r+8)
We can plug in for r but we still have variables t and d left. d=r*t. If we were to substitute for d we could cancel out t leaving us with just t, as we are looking for the time it took him to bike to his friends house.
t-1 = d/(r+8)
t-1 = r*t/(72+8)
t-1 = 72*t/(80)
80(t-1) = 72t
80t-80=72t
8t=80
t=10
SUFFICIENT

(C)
Intern
Joined: 11 Jul 2013
Posts: 34
Followers: 0

Kudos [?]: 2 [0], given: 34

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

24 Oct 2013, 21:41
WholeLottaLove wrote:
Mark biked from his house to his friend's house in how many hours?

Time = Distance/Speed

(1) Mark bikes at an average speed of 72 blocks per hour.
There is no information given about the distance Mark has to travel. All we know is that r=72
INSUFFICIENT

(2) If Mark could bike an extra 8 blocks for each hour, he would have arrived at his friend's place 1 hour earlier
t-1 = d/(r+8)
We can try and plug in various other distance/time/rate formulas to try and cancel out variables but it's unlikely that will leave us with only one given that there are three variables to plug in for.
INSUFFICIENT

1+2) r=72 and t-1 = d/(r+8)
We can plug in for r but we still have variables t and d left. d=r*t. If we were to substitute for d we could cancel out t leaving us with just t, as we are looking for the time it took him to bike to his friends house.
t-1 = d/(r+8)
t-1 = r*t/(72+8)
t-1 = 72*t/(80)
80(t-1) = 72t
80t-80=72t
8t=80
t=10
SUFFICIENT

(C)

if we take only second statement
(x+8)(t-1)=distance to his friends home=xt.................cant we find t from here ?
what am i doing wrong
Math Expert
Joined: 02 Sep 2009
Posts: 33037
Followers: 5760

Kudos [?]: 70588 [0], given: 9849

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

25 Oct 2013, 01:59
Expert's post
tyagigar wrote:
WholeLottaLove wrote:
Mark biked from his house to his friend's house in how many hours?

Time = Distance/Speed

(1) Mark bikes at an average speed of 72 blocks per hour.
There is no information given about the distance Mark has to travel. All we know is that r=72
INSUFFICIENT

(2) If Mark could bike an extra 8 blocks for each hour, he would have arrived at his friend's place 1 hour earlier
t-1 = d/(r+8)
We can try and plug in various other distance/time/rate formulas to try and cancel out variables but it's unlikely that will leave us with only one given that there are three variables to plug in for.
INSUFFICIENT

1+2) r=72 and t-1 = d/(r+8)
We can plug in for r but we still have variables t and d left. d=r*t. If we were to substitute for d we could cancel out t leaving us with just t, as we are looking for the time it took him to bike to his friends house.
t-1 = d/(r+8)
t-1 = r*t/(72+8)
t-1 = 72*t/(80)
80(t-1) = 72t
80t-80=72t
8t=80
t=10
SUFFICIENT

(C)

if we take only second statement
(x+8)(t-1)=distance to his friends home=xt.................cant we find t from here ?
what am i doing wrong

_________________
Manager
Joined: 24 Apr 2013
Posts: 71
Location: United States
Followers: 0

Kudos [?]: 10 [0], given: 23

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

27 Oct 2013, 03:21
For st 1, don't we have to know that the rate is uniform during the entire distance to be able to compute the time?
_________________

Struggling: make or break attempt

Math Expert
Joined: 02 Sep 2009
Posts: 33037
Followers: 5760

Kudos [?]: 70588 [0], given: 9849

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

27 Oct 2013, 06:54
Expert's post
SaraLotfy wrote:
For st 1, don't we have to know that the rate is uniform during the entire distance to be able to compute the time?

(1) says "Mark bikes at an average speed of 72 blocks per hour".
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 9642
Followers: 465

Kudos [?]: 120 [0], given: 0

Re: Mark biked from his house to his friend's house in how many [#permalink]

### Show Tags

15 Jan 2015, 13:50
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.
_________________
Re: Mark biked from his house to his friend's house in how many   [#permalink] 15 Jan 2015, 13:50
Similar topics Replies Last post
Similar
Topics:
2 In the morning, John drove to his mother's house in the 3 22 Mar 2013, 13:01
178 If it took Carlos 1/2 hour to cycle from his house to 43 23 Sep 2010, 14:10
14 If it took Carol 1/2 hour to cycle from his house to the 7 13 Nov 2011, 02:16
1 How many hours did it take Helen to drive from her house to 7 23 Jul 2008, 22:50
1 Patrick is cleaning his house in anticipation of the arrival 2 16 Nov 2007, 06:30
Display posts from previous: Sort by