• Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • 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
  • 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
  • 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
  • examPAL
    Most awarded test prep in the world
    Now free for 30 days

    Available with Beat the GMAT members only code

    MORE DETAILS
    examPAL
  • 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

OG question 134 - estimated avg speed

This topic has 3 expert replies and 1 member reply
NadineKh Newbie | Next Rank: 10 Posts Default Avatar
Joined
28 Jul 2017
Posted:
5 messages

OG question 134 - estimated avg speed

Post Tue Aug 15, 2017 1:00 am
In planning for a car trip, Joan estimated both the distance of the trip, in miles, and her average speed, in miles per hour. She accurately divided her estimated distance by her estimated average speed to obtain an estimate for the time, in hours, that the trip would take. Was her estimate within 0.5 hour of the actual time that the trip took?
(1) Joan’s estimate for the distance was within 5 miles of the actual distance.
(2) Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.

Answer: E

How would you rephrase the problem and how would you solve it?
I'm trying to find a more systematic way to solve this type of problem than trying numbers.

Thank you!

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post Wed Nov 15, 2017 4:35 pm
NadineKh wrote:
In planning for a car trip, Joan estimated both the distance of the trip, in miles, and her average speed, in miles per hour. She accurately divided her estimated distance by her estimated average speed to obtain an estimate for the time, in hours, that the trip would take. Was her estimate within 0.5 hour of the actual time that the trip took?
(1) Joan’s estimate for the distance was within 5 miles of the actual distance.
(2) Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.

Target question: Was Joan's ESTIMATE within 0.5 hour of the ACTUAL TIME that the trip took?

Statement 1: Joan’s ESTIMATE for the distance was within 5 miles of the ACTUAL distance.
Travel time = distance/speed

Statement 1 provides information regarding the accuracy of Joan's estimation of the travel distance, BUT it does not provide any information regarding her accuracy in estimating her speed.
As such, statement 1 is NOT SUFFICIENT

Statement 2: Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.
Statement 2 provides information regarding the accuracy of Joan's estimation of her average speed, BUT it does not provide any information regarding her accuracy in estimating the travel distance.
As such, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Let's test some numbers.
There are several possible scenarios that satisfy BOTH statements. Here are two:
Case a: Joan's estimates were PERFECTLY accurate. In this case, her ACTUAL travel time was definitely WITHIN 0.5 hours of her ESTIMATED travel.

Case b: Joan's ESTIMATED distance and average speed were 8 miles and 8 miles per hour respectively, and the ACTUAL distance and average speed were 5 miles and 1 mile per hour respectively. So, Joan's ESTIMATED travel time = 8/8 = 1 hour, and her ACTUAL travel time = 5/1 = 5 hours. In this case, Joan's ACTUAL travel time was NOT WITHIN 0.5 hours of her ESTIMATED travel.

Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

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

Check out the online reviews of our course
Come see 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!
NadineKh Newbie | Next Rank: 10 Posts Default Avatar
Joined
28 Jul 2017
Posted:
5 messages
Post Tue Aug 15, 2017 10:19 am
Thank you very much!!

It also helped me interpreting it more intuitively: since we have delta (differences between estimation and reality) in both numerator and denominator, we can't have an idea of the % deviation without knowing the value of the ratio.

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post Tue Aug 15, 2017 9:38 am
NadineKh wrote:
In planning for a car trip, Joan estimated both the distance of the trip, in miles, and her average speed, in miles per hour. She accurately divided her estimated distance by her estimated average speed to obtain an estimate for the time, in hours, that the trip would take. Was her estimate within 0.5 hour of the actual time that the trip took?
(1) Joan’s estimate for the distance was within 5 miles of the actual distance.
(2) Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.

Answer: E

How would you rephrase the problem and how would you solve it?
I'm trying to find a more systematic way to solve this type of problem than trying numbers.

Thank you!
Well, I'm not sure I'd bother rephrasing this one. Here's how I think about it: you can dismiss each statement on its own almost immediately. The first statement tells you nothing about speed and the second tells you nothing about distance.

Together, we want to see if we can get a YES and a No to the original question. Well, we can obviously get a YES - it's possible that Joan estimated the distance and the speed with uncanny precision, getting both on the nose, and so she'd have gotten the time on the nose as well. So in this case, YES, her estimate would be within .5 hours of the actual time.

So all we need is a NO.
Actual distance = 5
Joan's estimate = 10

Actual speed = 20mph
Joan's estimate = 10mph

Actual Time = 5/20 = .25 hours
Joan's estimate = 10/10 = 1 hour
1 - .25 = .75, so NO, her estimate is not within .5 hours. Together the statements are not sufficient. The answer is E

_________________
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course

  • +1 Upvote Post
  • Quote
  • Flag
Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!

GMAT/MBA Expert

Post Tue Aug 15, 2017 10:00 am
Come to think of it, we don't have to think about this one very hard.

Together:
Scenario 1: She gets the distance and the rate exactly right - YES, she's within 5. hours of the actual time.

Scenario 2: actual rate = 0; estimated rate = 10. Clearly, NO, she's not within .5 hours of the actual time, no matter the distance. She's not moving.

Answer is E

_________________
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course

  • +1 Upvote Post
  • Quote
  • Flag
Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!

Best Conversation Starters

1 lheiannie07 108 topics
2 Roland2rule 63 topics
3 ardz24 63 topics
4 LUANDATO 50 topics
5 AAPL 42 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description GMATGuruNY

The Princeton Review Teacher

152 posts
2 image description Jeff@TargetTestPrep

Target Test Prep

106 posts
3 image description Rich.C@EMPOWERgma...

EMPOWERgmat

104 posts
4 image description Scott@TargetTestPrep

Target Test Prep

96 posts
5 image description Max@Math Revolution

Math Revolution

87 posts
See More Top Beat The GMAT Experts