• 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

Vivian drives to her sister's house and back. She takes the

This topic has 5 expert replies and 0 member replies

Vivian drives to her sister's house and back. She takes the

Post

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

Difficult



Princeton Review

Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?

A. 50
B. 58.3
C. 60
D. 61.7
E. 70

OA B

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post
AAPL wrote:
Princeton Review

Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?

A. 50
B. 58.3
C. 60
D. 61.7
E. 70
One approach is to assign a "nice" value (one that works well with 50 mph and 70 mph) to the distance her sister's house.
So, let's say the distance is 350 miles

Average speed = (total distance traveled)/(total travel time)

TOTAL distance = 350 miles + 350 miles = 700 miles

Now let's calculate the TOTAL travel time.

time = distance/speed
So, travel time TO her sister's house = 350/50 = 7 hours
And travel time FROM her sister's house = 350/70 = 5 hours
So, TOTAL travel time = 7 hours + 5 hours = 12 hours

So, average speed = 700 miles/12 hours
= 700/12 miles per hour
= 350/6 miles per hour
= 175/3 miles per hour
= 58 1/3 miles per hour
≈ 58.3333 miles per hour

Answer: B

_________________
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
AAPL wrote:
Princeton Review

Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?

A. 50
B. 58.3
C. 60
D. 61.7
E. 70
When the same distance is traveled at two different speeds, the average speed for the entire trip will be a bit LESS than the average of the two speeds.
Since (70+50)/2 = 60, the average speed for Vivian's's entire trip must be a bit less than 60.

The correct answer is B.

_________________
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
AAPL wrote:
Princeton Review

Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?

A. 50
B. 58.3
C. 60
D. 61.7
E. 70
Alternate way: UNITS CONTROL, one of the most powerful tools of our method!
$$? = {{{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{miles}}} \over {{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}}}$$
$$350\,\,{\rm{miles}}\,\,\left( {{\rm{arbitrary!}}} \right)\,\,\,\left\{ \matrix{
\,{\rm{out}}:\,\,350\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {50\,\,{\rm{miles}}}}\matrix{
\nearrow \cr
\nearrow \cr

} } \right)\,\,\,\,\, = \,\,7\,{\rm{h}} \hfill \cr
\,{\rm{back}}:\,\,350\,\,{\rm{miles}}\,\,\left( {{{1\,\,{\rm{h}}} \over {70\,\,{\rm{miles}}}}\matrix{
\nearrow \cr
\nearrow \cr

} } \right)\,\, = \,\,5\,{\rm{h}} \hfill \cr} \right.\,\,\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,{\rm{total}}\,\,{\rm{\# }}\,\,{\rm{hours}}\,\, = \,12\,{\rm{h}}$$
Obs.: arrows indicate licit converters.
$$? = {{2 \cdot 350} \over {12}} = {{300 + 48 + 2} \over 6} = 58{1 \over 3}\,\,\,\left[ {{\rm{mph}}} \right]$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.

_________________
Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br

  • +1 Upvote Post
  • Quote
  • Flag
Post
AAPL wrote:
Princeton Review

Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?

A. 50
B. 58.3
C. 60
D. 61.7
E. 70
We can let d = the distance one way and use the formula: average rate = total distance/total time:

average rate = 2d/(d/50 + d/70)

average rate = 2d/(7d/350 + 5d/350)

average rate = 2d/(12d/350)

average rate = 700d/(12d) = 58.3

Answer: B

_________________
Scott Woodbury-Stewart Founder and CEO

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post
Hi All,

We're told that Vivian drives to her sister's house and back. She takes the exact same route both ways; on the trip out she drives an average speed of 50 miles per hour and on the trip back she drives an average speed of 70 miles per hour. We're asked for her approximate average speed for the round trip in miles per hour. This question can be solved in a couple of different ways. Sometimes that answer choices are 'spread out' in such a way that you can avoid almost all of the 'math' and use a 'logic shortcut' to get to the correct answer.

To start, since Vivian is driving the SAME distance in each direction, it will take her MORE time travel that distance at 50 miles/hour than it will take her to travel at 70 miles/hour. This makes this a 'Weighted Average' scenario - meaning that her average speed will be CLOSER to 50 miles/hour than it will be to 70 miles/hour. We can eliminate Answers C, D and E.

We also know that she travels at 70 miles/hour for some of the trip, so her average cannot be 50 miles/hour (logically, the speed must be greater than that), so we can eliminate Answer A. There's only one answer remaining...

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

_________________
Contact Rich at Rich.C@empowergmat.com

  • +1 Upvote Post
  • Quote
  • Flag
  • 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
  • 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
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • 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
  • 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
  • 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
  • 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
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh

Top First Responders*

1 fskilnik@GMATH 55 first replies
2 GMATGuruNY 52 first replies
3 Brent@GMATPrepNow 51 first replies
4 Jay@ManhattanReview 39 first replies
5 Rich.C@EMPOWERgma... 23 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 Scott@TargetTestPrep

Target Test Prep

198 posts
2 image description fskilnik@GMATH

GMATH Teacher

154 posts
3 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

97 posts
4 image description Max@Math Revolution

Math Revolution

89 posts
5 image description GMATGuruNY

The Princeton Review Teacher

76 posts
See More Top Beat The GMAT Experts