• EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • 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
  • 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
  • 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
  • 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
  • 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

Why does time matter

This topic has 2 expert replies and 1 member reply
MalcolmW Junior | Next Rank: 30 Posts Default Avatar
Joined
01 Nov 2015
Posted:
20 messages

Why does time matter

Post Tue Nov 17, 2015 6:16 pm
On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

I chose A as I normally practice not having to go into depth with solving problems to save time. I thought statement 2 gave me information that wasn't needed. Can someone explain the answer?

  • +1 Upvote Post
  • Quote
  • Flag
Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
MalcolmW Junior | Next Rank: 30 Posts Default Avatar
Joined
01 Nov 2015
Posted:
20 messages
Post Sat Nov 21, 2015 11:49 pm
ill be taking my test on 12/12 i just heard of this method. I'm not sure if that is enough time to implement it into my practice/studying.
Max@Math Revolution wrote:
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

If we modify the original condition, vt=50(v:velocity, t:time taken), there are 2 variables (v,t) and one equations (yt=50) and 2 equations, giving a high chance (D) will be our answer.
Condition 1) t=54 (30min+24min)
Condition 2) t=54min
Each are sufficient, making the answer (D).

For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Max@Math Revolution Legendary Member
Joined
24 Jul 2015
Posted:
858 messages
Followed by:
22 members
Upvotes:
19
GMAT Score:
Most Active Expert
Post Sat Nov 21, 2015 9:09 am
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

If we modify the original condition, vt=50(v:velocity, t:time taken), there are 2 variables (v,t) and one equations (yt=50) and 2 equations, giving a high chance (D) will be our answer.
Condition 1) t=54 (30min+24min)
Condition 2) t=54min
Each are sufficient, making the answer (D).

For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.

_________________

Math Revolution
Finish GMAT Quant Section with 10 minutes to spare.
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo
Email to : info@mathrevolution.com

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post Tue Nov 17, 2015 8:30 pm
MalcolmW wrote:
On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of 60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles per hour.
(2) She drove a total of 54 minutes.
Target question: What was Mary's average speed for the 50-mile trip?

Average speed = (total distance)/(total travel time)
= (50 miles)/(total travel time)

As you can see, we need only determine the total travel time.

Statement 1: She drove 30 miles at an average speed of 60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles per hour.
For both parts of her journey, we COULD determine the travel time, so we COULD find the total travel time, which means we COULD calculate Mary's average speed
Since we COULD answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: She drove a total of 54 minutes.
Perfect! Her total travel time is 54 minutes, so we COULD calculate Mary's average speed
Since we COULD answer the target question with certainty, statement 2 is SUFFICIENT

Answer = D

Cheers,
Brent

_________________
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!

Best Conversation Starters

1 Roland2rule 161 topics
2 lheiannie07 110 topics
3 ardz24 56 topics
4 LUANDATO 53 topics
5 Vincen 50 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

151 posts
2 image description Jeff@TargetTestPrep

Target Test Prep

145 posts
3 image description GMATGuruNY

The Princeton Review Teacher

114 posts
4 image description Rich.C@EMPOWERgma...

EMPOWERgmat

111 posts
5 image description Scott@TargetTestPrep

Target Test Prep

98 posts
See More Top Beat The GMAT Experts