It is currently 19 Oct 2017, 04:23

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

Events & Promotions in June
Open Detailed Calendar

Cole drove from home to work at an average speed of 75 kmh. He then

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

Hide Tags

Intern
Intern
avatar
Joined: 10 Sep 2015
Posts: 26

Kudos [?]: 26 [0], given: 5

Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 15 Sep 2015, 13:44
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

70% (03:02) correct 30% (03:17) wrong based on 139 sessions

HideShow timer Statistics

Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78

Source: GMAT Prep Now - http://www.gmatprepnow.com/module/gmat- ... /video/914
[Reveal] Spoiler: OA

Kudos [?]: 26 [0], given: 5

Intern
Intern
avatar
Joined: 10 Sep 2015
Posts: 26

Kudos [?]: 26 [0], given: 5

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 15 Sep 2015, 13:52
I tried solving the question by starting with this:
time to work + time home = 2
d/75 + d/105 = 2
105d/7875 + 75d/7875 = 15750
180d/7875 = 15750
180d = 7875*15750
I used my calculator for the rest and got d = 689062.5 which is obviously too big to work with the question.
So I stopped.
What went wrong?

Kudos [?]: 26 [0], given: 5

Intern
Intern
avatar
Joined: 14 Jul 2015
Posts: 14

Kudos [?]: 16 [0], given: 8

Location: United Arab Emirates
Concentration: International Business, General Management
GMAT 1: 660 Q49 V32
WE: Business Development (Energy and Utilities)
Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 15 Sep 2015, 14:55
Let the distance one way be x
Time from home to work = x/75
Time from work to home = x/105
Total time = 2 hrs
(x/75) + (x/105)= 2
Solving for x, we get x = 175/2

Time from home to work in minutes= (175/2)*60/75 = 70 minutes

Ans= B

Kudos [?]: 16 [0], given: 8

1 KUDOS received
Intern
Intern
avatar
Joined: 14 Jul 2015
Posts: 14

Kudos [?]: 16 [1], given: 8

Location: United Arab Emirates
Concentration: International Business, General Management
GMAT 1: 660 Q49 V32
WE: Business Development (Energy and Utilities)
Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 15 Sep 2015, 14:57
1
This post received
KUDOS
skylimit wrote:
I tried solving the question by starting with this:
time to work + time home = 2
d/75 + d/105 = 2
105d/7875 + 75d/7875 = 15750
180d/7875 = 15750
180d = 7875*15750
I used my calculator for the rest and got d = 689062.5 which is obviously too big to work with the question.
So I stopped.
What went wrong?



The error lies in your 2nd step- 105d/7875 + 75d/7875 = 15750

It should be 105d/7875 + 75d/7875 = 2

A better approach would be to take the common factors out. This way the calculation becomes much simpler. In this case taking common factor "15" out we get:

(1/15)*[(d/5)+(d/7)]= 2 --> (d/5)+(d/7)=30; which is much easier to solve manually. Remember, if you think you need a calculator on any GMAT question then probably your approach is not correct. There is always a way around.

Kudos [?]: 16 [1], given: 8

Intern
Intern
avatar
Joined: 10 Sep 2015
Posts: 26

Kudos [?]: 26 [0], given: 5

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 15 Sep 2015, 15:12
sunnysid wrote:
skylimit wrote:
I tried solving the question by starting with this:
time to work + time home = 2
d/75 + d/105 = 2
105d/7875 + 75d/7875 = 15750
180d/7875 = 15750
180d = 7875*15750
I used my calculator for the rest and got d = 689062.5 which is obviously too big to work with the question.
So I stopped.
What went wrong?



The error lies in your 2nd step- 105d/7875 + 75d/7875 = 15750

It should be 105d/7875 + 75d/7875 = 2

A better approach would be to take the common factors out. This way the calculation becomes much simpler. In this case taking common factor "15" out we get:

(1/15)*[(d/5)+(d/7)]= 2 --> (d/5)+(d/7)=30; which is much easier to solve manually. Remember, if you think you need a calculator on any GMAT question then probably your approach is not correct. There is always a way around.


Shoot! Nice catch. Thanks

Kudos [?]: 26 [0], given: 5

2 KUDOS received
Intern
Intern
avatar
Joined: 20 Aug 2015
Posts: 5

Kudos [?]: 5 [2], given: 83

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 16 Sep 2015, 01:36
2
This post received
KUDOS
1
This post was
BOOKMARKED
[quote="skylimit"]Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78

Hi All,

Here is my first post...

I prefer to use the ratio approach when it is possible, in this case it is.

The ratios between the speeds Work:Home = 75:105 = 5:7
Given that the distance in both directions is the same, the ratios of times becomes Work:Home = 7:5 (inverse)

The total time is given 2 hours ==> , so: 2/12 *7 = 14/12 hours ==> Multiple by 5 to get minutes = 70/60 ==> Answer is 70 minutes.

Kudos [?]: 5 [2], given: 83

Intern
Intern
avatar
Joined: 10 Sep 2015
Posts: 26

Kudos [?]: 26 [0], given: 5

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 16 Sep 2015, 09:07
zurvy wrote:
The total time is given 2 hours ==> , so: 2/12 *7 = 14/12 hours ==> Multiple by 5 to get minutes = 70/60 ==> Answer is 70 minutes.


The inverse method is interesting and it seems pretty fast too.
I just don't understand the very last part above.
Why did you multiply 2/12 by 7 and then multiply by 5 to get minutes?

Kudos [?]: 26 [0], given: 5

1 KUDOS received
Intern
Intern
avatar
Joined: 20 Aug 2015
Posts: 5

Kudos [?]: 5 [1], given: 83

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 16 Sep 2015, 23:34
1
This post received
KUDOS
skylimit wrote:
zurvy wrote:
The total time is given 2 hours ==> , so: 2/12 *7 = 14/12 hours ==> Multiple by 5 to get minutes = 70/60 ==> Answer is 70 minutes.


The inverse method is interesting and it seems pretty fast too.
I just don't understand the very last part above.
Why did you multiply 2/12 by 7 and then multiply by 5 to get minutes?



Hi there,

The ratio of time is as explained 5:7 during the entire trip , and it took a total of 2 hours ==> Imagine it like this, you have to split the 2 hours
with a ratio of 5:7 ==> The total parts would be in this case 5+7 = 12 ==> so The total time has to be divided first by 12, and then multiplied by 5.
If I told you to split 24 apples among two persons with a ratio of 5:7, you would first divide 24/12 (12=7+5) and than multiple by 5 and 7 respectively to get the answer.
24/12 * 5 = 10 for one person 24/12 * 7 = 14 for the other making a total of 24 apples.


Regarding the multiplication by 5, you need to convert 14/12 to fractions of 60 (so you get the minutes).
(5*14/5*12 = 70/60)
Or you could, 14/12 = 7/6 hour = 1 1/6 hour = 1 hour and 10 minutes = 70/60 hour (its just playing with fractions, and with time, having a denominator of 60, always
gives you the number of minutes at the top)

Kudos [?]: 5 [1], given: 83

Intern
Intern
avatar
Joined: 10 Sep 2015
Posts: 26

Kudos [?]: 26 [0], given: 5

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 17 Sep 2015, 10:06
zurvy wrote:
skylimit wrote:
zurvy wrote:
The total time is given 2 hours ==> , so: 2/12 *7 = 14/12 hours ==> Multiple by 5 to get minutes = 70/60 ==> Answer is 70 minutes.


The inverse method is interesting and it seems pretty fast too.
I just don't understand the very last part above.
Why did you multiply 2/12 by 7 and then multiply by 5 to get minutes?



Hi there,

The ratio of time is as explained 5:7 during the entire trip , and it took a total of 2 hours ==> Imagine it like this, you have to split the 2 hours
with a ratio of 5:7 ==> The total parts would be in this case 5+7 = 12 ==> so The total time has to be divided first by 12, and then multiplied by 5.
If I told you to split 24 apples among two persons with a ratio of 5:7, you would first divide 24/12 (12=7+5) and than multiple by 5 and 7 respectively to get the answer.
24/12 * 5 = 10 for one person 24/12 * 7 = 14 for the other making a total of 24 apples.


Regarding the multiplication by 5, you need to convert 14/12 to fractions of 60 (so you get the minutes).
(5*14/5*12 = 70/60)
Or you could, 14/12 = 7/6 hour = 1 1/6 hour = 1 hour and 10 minutes = 70/60 hour (its just playing with fractions, and with time, having a denominator of 60, always
gives you the number of minutes at the top)


Thanks zurvy!
I didn't realize you multiplied by 5 to get a denominator of 60.
Nice solution

Kudos [?]: 26 [0], given: 5

Director
Director
avatar
G
Joined: 07 Dec 2014
Posts: 812

Kudos [?]: 247 [0], given: 12

Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 17 Sep 2015, 17:00
let t=time to work
time to home (derived from inverse kmh ratio)=75t/105➡5t/7
t+5t/7=2 hours total time
t=7/6 hours➡70 minutes

Kudos [?]: 247 [0], given: 12

Intern
Intern
avatar
Joined: 19 Mar 2014
Posts: 5

Kudos [?]: 1 [0], given: 3

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 18 Sep 2015, 22:25
[quote="skylimit"]Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78




Answer : B

First round distance travelled (say) = d
Speed = 75 k/h
Time taken, T2 = d/75 hr

Second round distance traveled = d (same distance)
Speed = 105 k/h
Time taken, T2 = d/105 hr

Total time taken = 2 hrs
Therefore , 2 = d/75 + d/105
LCM of 75 and 105 = 525

2= d/75 + d/105
=> 2 = 7d/525 + 5d/525
=> d = 525 / 6 Km

Therefore, T1= d/75
=> T1 = 525 / (6 x 75)
=> T1 = (7 x 60) / 6 -- in minutes
=> T1 = 70 minutes.

Kudos [?]: 1 [0], given: 3

Intern
Intern
User avatar
Joined: 21 Feb 2016
Posts: 9

Kudos [?]: [0], given: 104

Location: United States (MA)
Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 30 Jun 2016, 11:53
Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78

Round-trip average speed: (2*75*105)/(75+105)=525/6
Round-trip time=2 hrs given
So round-trip distance=(526/6)*2=175 kms
Single-trip distance=175/2 kms...Time taken to cover this distance at 75kmph= (175/2)/75 hrs=70 mins.

Kudos [?]: [0], given: 104

Manager
Manager
avatar
B
Joined: 30 Apr 2013
Posts: 57

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

CAT Tests
Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 03 Oct 2017, 01:55
Time = distance /speed

So Lets consider D =100

Therefore , 100/75(60) +100/105(50)= 120 mins

Is the right way of thinking ?

Can someone please explain this with logic not formulas

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

Manager
Manager
User avatar
S
Joined: 22 May 2015
Posts: 74

Kudos [?]: 15 [0], given: 22

Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 03 Oct 2017, 05:22
santro789 wrote:
Time = distance /speed

So Lets consider D =100

Therefore , 100/75(60) +100/105(50)= 120 mins

Is the right way of thinking ?

Can someone please explain this with logic not formulas


It is incorrect to assume the value of distance D as we have a constrain on time ( t1+t2 = 2 hours ).

We know the avg speed for first half is 75kmph => D = 75 * T1
We also know the avg speed for second half is 105kmph => D = 105*T2

Since the distance is same we can equate the above equations 75*T1 = 105*T2 => 5T1=7T2.
Now we know the total time taken is 2 hours => T1+T2 = 2
On solving we will get T1 = 7/6 hours which is 70 minutes.
_________________

Consistency is the Key

Kudos [?]: 15 [0], given: 22

Expert Post
1 KUDOS received
Target Test Prep Representative
User avatar
S
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 1634

Kudos [?]: 837 [1], given: 2

Location: United States (CA)
Re: Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 05 Oct 2017, 10:12
1
This post received
KUDOS
Expert's post
skylimit wrote:
Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78



We use the formula distance = rate x time, or equivalently, time = distance/rate. We can let the distance either way = d; thus, Cole’s time from home to work is d/75 and his time from work to home is d/105. The total travel time is given as 2 hours, so we have:

d/75 + d/105 = 2

Multiplying the entire equation by 525, we have:

7d + 5d = 1050

12d = 1050

d = 1050/12 = 525/6 = 175/2 km

Thus, it took him (175/2)/75 = 175/150 = 7/6 hours = 7/6 x 60 = 70 minutes.

Answer: B
_________________

Scott Woodbury-Stewart
Founder and CEO

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

Kudos [?]: 837 [1], given: 2

Intern
Intern
avatar
B
Joined: 09 Dec 2013
Posts: 18

Kudos [?]: [0], given: 193

Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 05 Oct 2017, 17:19
zurvy wrote:
skylimit wrote:
Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78

Hi All,

Here is my first post...

I prefer to use the ratio approach when it is possible, in this case it is.

The ratios between the speeds Work:Home = 75:105 = 5:7
Given that the distance in both directions is the same, the ratios of times becomes Work:Home = 7:5 (inverse)

The total time is given 2 hours ==> , so: 2/12 *7 = 14/12 hours ==> Multiple by 5 to get minutes = 70/60 ==> Answer is 70 minutes.



Very good explanation though. But I did not understand the purpose of taking the inverse of the ratio from 5:7
Don't we have to calculate time taken from home to work?
TIA

Kudos [?]: [0], given: 193

Director
Director
avatar
P
Joined: 22 May 2016
Posts: 810

Kudos [?]: 262 [0], given: 549

Cole drove from home to work at an average speed of 75 kmh. He then [#permalink]

Show Tags

New post 05 Oct 2017, 19:03
skylimit wrote:
Cole drove from home to work at an average speed of 75 kmh. He then returned home at an average speed of 105 kmh. If the round trip took a total of 2 hours, how many minutes did it take Cole to drive to work?
A) 66
B) 70
C) 72
D) 75
E) 78

Source: GMAT Prep Now - http://www.gmatprepnow.com/module/gmat- ... /video/914

I avoid division if I can in RTD problems. I solved for time with multiplication. It's fast.

Total time = 2 hours

Let time from home to work = x
So time from work to home = (2-x)

Rate, home to work = 75 kmh
Rate, work to home = 105 kmh

\(r*t=D\)

D, home to work: (75*x)
D, work to home: (105)*(2-x)

\(D\) is equal both ways, hence

\(75x = (105)(2-x)\)
\(75x = 210 - 105x\)
\(180x = 210\)

\(x = \frac{210}{180} = \frac{21}{18} =\frac{7}{6}hrs\)

Any fraction of an hour can be multiplied by 60 to obtain minutes.

\(x =\frac{7}{6}hrs * 60\) = 70 minutes

Answer B

Kudos [?]: 262 [0], given: 549

Cole drove from home to work at an average speed of 75 kmh. He then   [#permalink] 05 Oct 2017, 19:03
Display posts from previous: Sort by

Cole drove from home to work at an average speed of 75 kmh. He then

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


cron

GMAT Club MBA Forum Home| About| Terms and Conditions| 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®.