Find all School-related info fast with the new School-Specific MBA Forum
Learn more about the recent changes... close

It is currently 22 May 2013, 12:47
Customize  |  Hide

Search
Register
New posts
Unanswered

A certain car averages 25 miles per gallon when driving in

  Question banks Downloads My Bookmarks Reviews  
  Oldest Best Reply
Search for:
 
Print view
First unread post
Author Message
TAGS:
Intern
Intern
Joined: 04 Jul 2010
Posts: 19
Followers: 0

Kudos [?]: 1 [0], given: 0

A certain car averages 25 miles per gallon when driving in [#permalink] New post 11 Aug 2010, 14:17
00:00

Question Stats:

57% (02:39) correct 42% (01:41) wrong based on 4 sessions
A certain car averages 25 miles per gallon when driving in the city and 40 miles per gallon when driving on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and then 50 miles on the highway?

A. 28
B. 30
C. 33
D. 36
E. 38
[Reveal] Spoiler: OA

Last edited by Bunuel on 30 Mar 2012, 10:36, edited 1 time in total.
Edited the question and added the OA
1 KUDOS received
GMAT Club team member
User avatar
Joined: 02 Sep 2009
Posts: 11565
Followers: 1796

Kudos [?]: 9571 [1] , given: 826

GMAT Tests User CAT Tests
Top Member of the Month
Re: More Prep questions [#permalink] New post 11 Aug 2010, 17:56
1
This post received
KUDOS
A certain car averages 25 miles per gallon when driving in the city and 40 miles per gallon when driving on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and then 50 miles on the highway?

A. 28
B. 30
C. 33
D. 36
E. 38

Car averages x miles per gallon, means that 1 gallon is enough to drive x miles.

We are asked to find average miles per gallon (miles/gallon) --> average miles per gallon would be total miles driven divided by total gallons used (miles/gallon).

Total miles driven is 10+50=60.

As car averages 25 miles per gallon in the city for 10 miles in the city it will use 10/25=0.4 gallons;
As car averages 40 miles per gallon on the highway for 50 miles on the highway it will use 50/40=1.25 gallons;

So average miles per gallon equals to \frac{60}{0.4+1.25}\approx{36}

Answer: D.
_________________

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!


What are GMAT Club Tests?
25 extra-hard Quant Tests

Find out what's new at GMAT Club - latest features and updates

Manager
Manager
Joined: 12 Jul 2010
Posts: 70
Followers: 1

Kudos [?]: 2 [0], given: 3

Re: More Prep questions [#permalink] New post 19 Aug 2010, 23:37
Answer D

No of Miles per Gallon = Total no of miles/Total no of Gallons
=10+50/(10/25+50/40) ~ 36.3
Ms. Big Fat Panda
Ms. Big Fat Panda
User avatar
Status: Biting Nails Into Oblivion
Joined: 09 Jun 2010
Posts: 1859
Followers: 293

Kudos [?]: 1115 [0], given: 194

GMAT ToolKit User GMAT Tests User
Re: GMAT PREP PS [#permalink] New post 22 Aug 2010, 19:49
Average miles per gallon is given by: Total distance traveled/Total gallons used.

Total distance traveled is given to us and is equal to 10+50 = 60 miles

Total gallons used can be determined by reverse working the formula listed above.

Number of gallons in the city = Total distance / Average = \frac{10}{25}

Number of gallons in the highway = Total distance / Average = \frac{50}{40}

Total number of gallons = Sum of the above two quantities.

So the average overall

\frac{60}{\frac{10}{25} + \frac{5}{4}} = \frac{60}{\frac{2}{5} + \frac{5}{4}} =
\frac{60}{\frac{33}{20}} = \frac{1200}{33} = \frac{400}{11}

If you solve this you get 36.3636. So the answer is 36.
Manager
Manager
Joined: 21 Feb 2010
Posts: 216
Followers: 1

Kudos [?]: 10 [0], given: 1

GMAT Tests User
Re: GMAT PREP PS [#permalink] New post 22 Aug 2010, 20:06
i got 36 too using the same method as whiplash2411 did.
Manager
Manager
Joined: 27 May 2010
Posts: 205
Followers: 2

Kudos [?]: 7 [0], given: 3

GMAT Tests User
Re: GMAT PREP PS [#permalink] New post 22 Aug 2010, 20:22
10/25 => 2/5 gal

50/40 => 5/4 gal

Therefore the car travels 60 miles using 2/5 + 5/4

Calculating it gets 60/(33/20) => 36.36 miles/gal
Manager
Manager
User avatar
Joined: 15 Apr 2010
Posts: 200
Followers: 3

Kudos [?]: 14 [0], given: 29

GMAT Tests User
Re: Averages [#permalink] New post 14 Sep 2010, 02:23
D is closest to the correct decimal answer.... the way to solve is to find out total gallons of fuel used and total distance travelled. then divide the total distance 60 miles by X gallons.

to find X: we have 2 steps - 10/25 = 0.40 gallons is for city driving; 50/40=1.25 is for highway driving.

hence final answer = 60/1.65 which comes out to be ~36mpg. hope this is clear...
Manager
Manager
Joined: 14 Feb 2011
Posts: 203
Followers: 4

Kudos [?]: 42 [0], given: 3

GMAT Tests User
Re: Tough GMAT prep PS [#permalink] New post 19 Feb 2011, 11:01
For 10 miles, the fuel expended is 10/25 gallons = 0.4 gallons.
Similarly for 50 miles it is 50/40 gallon = 1.25 gallons
So for 60 miles total fuel spent is 1.65 gallons
and hence average miles per gallon = 60/1.65 = ~36
Manager
Manager
Joined: 26 Jan 2012
Posts: 78
Followers: 0

Kudos [?]: 8 [0], given: 14

Re: A certain car averages 25 miles per gallon when driving in [#permalink] New post 31 Dec 2012, 11:33
why does weighted average method fail? answer is 37.5 miles/hr. Please explain
Intern
Intern
Joined: 21 Mar 2009
Posts: 21
Followers: 0

Kudos [?]: 7 [0], given: 0

Re: A certain car averages 25 miles per gallon when driving in [#permalink] New post 31 Dec 2012, 11:45
ketanth wrote:
why does weighted average method fail? answer is 37.5 miles/hr. Please explain


Your question on weighted avergae is not clear. You need to find out the fractions summing up to 1, thats the basic requirement, which is not applicable here. See my soln, and let me know if you have any question:

Km/Gallon Km Gallon neded
City 25 10 10/25 = 2/5
Highway 40 50 50/40 = 5/4
Total 60 (8+25)/20 = 33/20

Mileage as asked = Total Km/Total Gallon = 60/(33/20) = 60*20/33 = 400/11 approx 38
Manager
Manager
Joined: 26 Jan 2012
Posts: 78
Followers: 0

Kudos [?]: 8 [0], given: 14

Re: A certain car averages 25 miles per gallon when driving in [#permalink] New post 31 Dec 2012, 19:34
maibhihun wrote:
ketanth wrote:
why does weighted average method fail? answer is 37.5 miles/hr. Please explain


Your question on weighted avergae is not clear. You need to find out the fractions summing up to 1, thats the basic requirement, which is not applicable here. See my soln, and let me know if you have any question:

Km/Gallon Km Gallon neded
City 25 10 10/25 = 2/5
Highway 40 50 50/40 = 5/4
Total 60 (8+25)/20 = 33/20

Mileage as asked = Total Km/Total Gallon = 60/(33/20) = 60*20/33 = 400/11 approx 38


Why cant we do the weighted average method:
(25X10+40X50)/(50+10) = 37,5 km/gallon

I understand your logic. I am trying to understand why weighted average method logic is false.
Re: A certain car averages 25 miles per gallon when driving in   [#permalink] 31 Dec 2012, 19:34
    Similar topics Author Replies Last post
Similar
Topics:
 New posts A certain car averages 25 miles per gallon of gasoline when mophead 3 28 Aug 2005, 06:36
New posts A certain car averages 25 miles per gallon when driven in flowers24 3 05 Aug 2006, 15:41
New posts a certain car averages 25 miles per gallon of gasoline when cejismundo 4 11 Sep 2006, 14:28
New posts A certain car averages 25 miles per gallon of gasline when Hermione 1 20 Oct 2006, 02:15
New posts 6 EXPERTS_POSTS_IN_THIS_TOPIC A certain car averages 25 miles per gallon of gasoline when enigma123 7 25 Feb 2012, 19:00
Display posts from previous: Sort by

A certain car averages 25 miles per gallon when driving in

  Question banks Downloads My Bookmarks Reviews  
Print view
First unread post

Moderators: Bunuel, VeritasPrepKarishma, IanStewart

Search for:


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.

Main navigation

GMAT Resources

Partners

MBA Resources

www.gmac.com|www.mba.com