In the morning, John drove to his mother's house in the village at an average speed of 60 kilometers per hour. When he was going back to town in the evening, he drove more cautiously and his speed was lower. If John went the same distance in the evening as in the morning, what was John's average speed for the entire trip?
(1) In the evening, John drove at a constant speed of 40 kilometers per hour.
(2) John's morning drive lasted 2 hours.
Can some experts find how the best Option become the correct answer?
OA A
In the morning, John drove to his mother's house
This topic has expert replies
-
- Moderator
- Posts: 7187
- Joined: Thu Sep 07, 2017 4:43 pm
- Followed by:23 members
GMAT/MBA Expert
- Jay@ManhattanReview
- GMAT Instructor
- Posts: 3008
- Joined: Mon Aug 22, 2016 6:19 am
- Location: Grand Central / New York
- Thanked: 470 times
- Followed by:34 members
Speed in the morning = 60 kmph;lheiannie07 wrote:In the morning, John drove to his mother's house in the village at an average speed of 60 kilometers per hour. When he was going back to town in the evening, he drove more cautiously and his speed was lower. If John went the same distance in the evening as in the morning, what was John's average speed for the entire trip?
(1) In the evening, John drove at a constant speed of 40 kilometers per hour.
(2) John's morning drive lasted 2 hours.
Can some experts find how the best Option become the correct answer?
OA A
Speed in the evening < 60 kmph
(1) In the evening, John drove at a constant speed of 40 kilometers per hour.
Say the distance of the village = 120 kilometers (LCM of 60 and 40; ease to deal with)
Time taken in the morning = Distance/ Speed = 120 / 60 = 2 hours
Time taken in the evening = Distance/ Speed = 120 / 40 = 3 hours
Average speed = Total distance / Total time = (120+120) / 5 = 240/5 = 48 kilometers per hour. Sufficient
(2) John's morning drive lasted 2 hours.
We have no information about the speed in the evening. Insufficient.
The correct answer: A
Hope this helps!
-Jay
_________________
Manhattan Review GMAT Prep
Locations: New York | New Delhi | Seoul | Cairo | and many more...
Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
GMAT/MBA Expert
- Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7243
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
We are given that John drives at a rate of 60 km per hour and drives at a lesser rate when driving again later. We also are given that the distances driven are the same and need to determine the average rate.lheiannie07 wrote:In the morning, John drove to his mother's house in the village at an average speed of 60 kilometers per hour. When he was going back to town in the evening, he drove more cautiously and his speed was lower. If John went the same distance in the evening as in the morning, what was John's average speed for the entire trip?
(1) In the evening, John drove at a constant speed of 40 kilometers per hour.
(2) John's morning drive lasted 2 hours.
We can use the formula:
average speed = total distance/total time
Statement One Alone:
In the evening, John drove at a constant speed of 40 kilometers per hour.
Since the distance each way is d, we can let time 1 = d/60, and time 2 = d/40; thus:
average speed = 2d/(d/60 + d/40)
average speed = 2d/(2d/120 + 3d/120)
average speed = 2d/(5d/120)
average speed = 240d/5d = 48
Statement one alone is sufficient to answer the question.
Statement Two Alone:
John's morning drive lasted 2 hours.
Knowing only the total time is not enough to determine the average speed.
Answer: A
Scott Woodbury-Stewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
- GMATGuruNY
- 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
When the SAME DISTANCE on the GMAT is traveled at two different speeds, the average speed for the entire trip will be just a bit closer to the lower speed than to the higher speed.lheiannie07 wrote:In the morning, John drove to his mother's house in the village at an average speed of 60 kilometers per hour. When he was going back to town in the evening, he drove more cautiously and his speed was lower. If John went the same distance in the evening as in the morning, what was John's average speed for the entire trip?
(1) In the evening, John drove at a constant speed of 40 kilometers per hour.
(2) John's morning drive lasted 2 hours.
The reason:
The journey at the lower speed takes LONGER than the journey at the higher speed.
Since more time is spent at the lower speed than at the higher speed, the average speed for the entire trip will be just a bit closer to the lower speed.
Put another way:
The average speed for the entire trip will be just a bit less than the AVERAGE of the lower speed and the higher speed.
Statement 1:
Since the same distance is traveled at 40 mph and at 60 mph, the average speed for the entire trip will be just a bit less than the average of 40 and 60:
(40+60)/2 = 50.
Thus, the average speed for the entire trip will be just a bit less than 50 mph.
SUFFICIENT.
Statement 2:
If the lower speed = 40 mph, then the average speed for the entire trip will be just a bit less than 50 mph, as in Statement 1.
If the lower speed = 50 mph, then the average speed for the entire trip will be just a bit less than 55 mph (the average of 50 and 60).
Since the average speed for the entire trip can be different values, INSUFFICIENT.
The correct answer is A.
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
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