GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 25 Aug 2019, 00:05

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Susan drove an average speed of 30 miles per hour for the

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Manager
Manager
avatar
S
Joined: 23 Sep 2016
Posts: 241
Reviews Badge
Susan drove an average speed of 30 miles per hour for the  [#permalink]

Show Tags

New post 27 Feb 2018, 22:38
1
anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55

IMO B .i solved this question by box method attached bellow:-
KUDOS iF YOU LIKE MY EXPLANATION. THANKS IN ADVANCE
Attachments

Screenshot (76).png
Screenshot (76).png [ 75.69 KiB | Viewed 1145 times ]

CEO
CEO
User avatar
V
Joined: 12 Sep 2015
Posts: 3922
Location: Canada
Re: Susan drove an average speed of 30 miles per hour for the  [#permalink]

Show Tags

New post 03 Apr 2018, 10:19
Top Contributor
anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55


Average speed = (TOTAL distance)/(TOTAL time)

TOTAL distance
Susan traveled 30 miles at a speed of 30mph, and 30 miles more at a speed of 60mph.
So, TOTAL distance = 30 miles + 30 miles = 60 miles

TOTAL time
TOTAL time = (time spent driving 30 mph) + (time spent driving 60 mph)
time = distance/speed
- Time spent driving 30 mph = 30 miles/30mph = 1 hour
- Time spent driving 60 mph = 30 miles/60mph = 0.5 hours
TOTAL time = (1 hour) + (0.5 hours) = 1.5 hours
----------------------------------

So, Average speed = (TOTAL distance)/(TOTAL time)
= 60 miles/1.5 hours
= 40 mph

Answer: B

Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
Image
SVP
SVP
User avatar
V
Status: It's near - I can see.
Joined: 13 Apr 2013
Posts: 1694
Location: India
Concentration: International Business, Operations
Schools: INSEAD Jan '19
GPA: 3.01
WE: Engineering (Real Estate)
Reviews Badge
Re: Susan drove an average speed of 30 miles per hour for the  [#permalink]

Show Tags

New post 14 Apr 2018, 23:04
anilnandyala wrote:
Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip

A. 35
B. 40
C. 45
D. 50
E. 55


Distance 1 = 30 miles

Speed 1 = 30 m/h

Time 1 = 30/30 = 1 hr

Distance 2 = 30 miles

Speed 2 = 60 m/h

Time 2 = 30/60 = 0.5 hr

Average speed = \(\frac{30 * 1 + 60 * 0.5}{1 + 0.5}\)

Avg Speed = 40 m/h

(B)
_________________
"Do not watch clock; Do what it does. KEEP GOING."
Intern
Intern
avatar
B
Joined: 20 Sep 2018
Posts: 6
Location: India
Concentration: Finance, Marketing
Schools: IIM
GPA: 3.68
Reviews Badge
Re: Susan drove an average speed of 30 miles per hour for the  [#permalink]

Show Tags

New post 01 Oct 2018, 10:52
If one is able to understand concepts of speed correctly. They can note that this is not the arithmetic mean ever(unless distance and speed for both journey's are equal). Averaging of speed works on Harmonic Mean. That is :( 2 x A x B) /(A+B)

Where A and B are 2 speed. Works always whether a person is following to-fro motion or running same distance with diff speeds.

Do Note : This doesn't work when 2 distances are different.
Manager
Manager
User avatar
B
Joined: 16 May 2017
Posts: 51
GPA: 3.8
WE: Medicine and Health (Health Care)
Re: Susan drove an average speed of 30 miles per hour for the  [#permalink]

Show Tags

New post 13 Oct 2018, 06:45
Avg. Speed= 2ab/(a+b)= 2*30*60/(30+60) = 40 mph.

Ans-B
GMAT Club Bot
Re: Susan drove an average speed of 30 miles per hour for the   [#permalink] 13 Oct 2018, 06:45

Go to page   Previous    1   2   [ 25 posts ] 

Display posts from previous: Sort by

Susan drove an average speed of 30 miles per hour for the

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne