BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Speed-Time Problem.

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 142
Joined: Sat Oct 20, 2012 3:31 am
Location: New Delhi
Thanked: 20 times
Followed by:3 members

Speed-Time Problem.

by aman88 » Thu Dec 27, 2012 11:25 am
When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?

A. 8v/3
B. 4v
C. 5v
D. 16v/3
E. 8v

OA C
Please let me know how to deal with this problem.

Thanks.
Top
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Thu Dec 27, 2012 4:34 pm
aman88 wrote:When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?

A. 8v/3
B. 4v
C. 5v
D. 16v/3
E. 8v

OA C
The portion in red omits the average speed for the entire 2m miles.
Could you please supply the missing information?
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Master | Next Rank: 500 Posts
Posts: 142
Joined: Sat Oct 20, 2012 3:31 am
Location: New Delhi
Thanked: 20 times
Followed by:3 members

by aman88 » Thu Dec 27, 2012 11:09 pm
GMATGuruNY wrote:
aman88 wrote:When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?

A. 8v/3
B. 4v
C. 5v
D. 16v/3
E. 8v

OA C
The portion in red omits the average speed for the entire 2m miles.
Could you please supply the missing information?
I am sorry. The question reads:

When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of 5v/3 miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Fri Dec 28, 2012 1:28 am
aman88 wrote:When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of 5v/3 miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?
Average speed for 2m miles = 5v/3 miles per hour
Hence, time taken to travel 2m miles = 2m/(5v/3) hours = 6m/5v hours

Average speed for first m miles = v miles per hour
Hence, time taken to travel first m miles = m/v hours

Hence, time taken to travel the final m miles = (6m/5v - m/v) hours = m/5v hours
Hence, average speed for the final m miles = m/(m/5v) mph = 5v miles per hour

The correct answer is C.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Fri Dec 28, 2012 6:15 am
aman88 wrote:When a car traveled from Town A to Town B without stopping, the car traveled a total of 2m miles, where m > 0. The car traveled the first m miles at an average speed of v miles per hour, and the car traveled the entire 2m miles at an average speed of 5v/3 miles per hour. What was the average speed of the car, in miles per hour, when it traveled the final m miles?

A. 8v/3
B. 4v
C. 5v
D. 16v/3
E. 8v
Let m=15 and v=3.
Time for the first m miles = d/r = m/v = 15/3 = 5 hours.
Time for the entire 2m miles = d/r = (2m)/(5v/3) = (2*15/( 5*3 / 3 ) = 6 hours.
Since the time for the entire 2m miles is 6 hours, and the time for the first m miles is 5 hours, the time for the last m miles = 6-5 = 1 hour.
Average speed for the last m miles = d/t = 15/1 = 15 miles per hour. This is our target.

Now we plug v=3 into the answers to see which yields our target of 15.
Only C works:
5v = 5*3 = 15.

The correct answer is C.
Last edited by GMATGuruNY on Mon Dec 31, 2012 9:37 am, edited 1 time in total.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Senior | Next Rank: 100 Posts
Posts: 56
Joined: Mon Sep 17, 2012 12:27 pm
Thanked: 13 times
Followed by:1 members
GMAT Score:710

by buzzdeepak » Fri Dec 28, 2012 9:26 am
Another way to explain the answer (personally, this works best for me). Hope this helps.

Set up the problem as R-T-D (Rate - Time - Distance)

R T D
First m miles v t1 m
Next m miles x t2 m
Total 5v/3 T 2m

Since total t = sum of the individual t's, we have:
t1+t2 = T
m/v + m/x = 2m/(5v/3)
Solve for x

I am including an image (apparently all the formatting is getting lost)

Image
[/img]
Top
Post new topic Post Reply
• Page 1 of 1