• NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    Hundreds of Questions Highly Detailed Reporting Expert Explanations TAKE A FREE GMAT QUIZ
  • 7 CATs FREE!
    If you earn 100 Forum Points

    Engage in the Beat The GMAT forums to earn
    100 points for $49 worth of Veritas practice GMATs FREE

    Veritas Prep
    VERITAS PRACTICE GMAT EXAMS
    Earn 10 Points Per Post
    Earn 10 Points Per Thanks
    Earn 10 Points Per Upvote
    REDEEM NOW

On a certain Monday, Carlos drove to work at an average

This topic has 2 expert replies and 1 member reply

On a certain Monday, Carlos drove to work at an average

Post

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

Difficult



Source: Veritas Prep

On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given

The OA is A

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post
BTGmoderatorLU wrote:
Source: Veritas Prep

On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given

The OA is A
[size=150]Average speed = (TOTAL distance)/TOTAL travel time)[/size]

Let d = the distance from work to home

Carlos drove to work at an average speed of 50 miles per hour
Time = distance/speed
So, travel time TO work = d/50 hours

Carlos drove home from work at an average speed of 70 miles per hour
So, travel time FROM work = d/70 hours

So, TOTAL travel time = d/50 + d/70
= 7d/350 + 5d/350 [rewrite with common denominators]
= 12d/350

Also, TOTAL distance = d + d = 2d

Which of the following is closest to his average speed for both trips combined?
Average speed = (TOTAL distance)/TOTAL travel time)
= (2d)/(12d/350)
= (2d)(350/12d)
= 700d/12d
= 700/12
= 350/6

STOP.
Since 360/60 = 60, we know that 350/6 will be LESS THAN 60

Answer: A

Cheers,
Brent

_________________
Brent Hanneson – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

GMAT/MBA Expert

Post
BTGmoderatorLU wrote:
Source: Veritas Prep

On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given
When the SAME DISTANCE is traveled at two different speeds, the average speed for the entire trip will be CLOSER TO THE LOWER SPEED than to the higher speed.
The reason:
The portion traveled at the lower speed takes LONGER.
Since more time is spent at the lower speed than at the higher speed, the average speed for the entire trip will be closer to the lower speed.
Here, halfway between the two speeds = the average of the two speeds = (50+70)/2 = 60.
To be closer to the lower speed and to the higher speed, the average speed for the entire trip must be LESS THAN 60.

The correct answer is A.

_________________
Mitch Hunt
Private Tutor for the GMAT and GRE
GMATGuruNY@gmail.com

If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon.

Available for tutoring in NYC and long-distance.
For more information, please email me at GMATGuruNY@gmail.com.
Student Review #1
Student Review #2
Student Review #3

  • +1 Upvote Post
  • Quote
  • Flag
Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.
Post
For these type of questions we can apply direct formula given below:

2ab/(a+b), where a & b are avg. speed. So 2x50x70/(120)= 58.33 (approx).

  • +1 Upvote Post
  • Quote
  • Flag
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • The Princeton Review
    FREE GMAT Exam
    Know how you'd score today for $0

    Available with Beat the GMAT members only code

    MORE DETAILS
    The Princeton Review

Top First Responders*

1 Jay@ManhattanReview 70 first replies
2 fskilnik@GMATH 50 first replies
3 Brent@GMATPrepNow 50 first replies
4 GMATGuruNY 33 first replies
5 Rich.C@EMPOWERgma... 27 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

Most Active Experts

1 image description fskilnik@GMATH

GMATH Teacher

106 posts
2 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

94 posts
3 image description Max@Math Revolution

Math Revolution

93 posts
4 image description Jay@ManhattanReview

Manhattan Review

82 posts
5 image description GMATGuruNY

The Princeton Review Teacher

77 posts
See More Top Beat The GMAT Experts