It is currently 21 Oct 2017, 18:24

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# A certain car averages 25 miles per gallon of gasoline when

Author Message
TAGS:

### Hide Tags

Director
Status: Finally Done. Admitted in Kellogg for 2015 intake
Joined: 25 Jun 2011
Posts: 533

Kudos [?]: 4124 [1], given: 217

Location: United Kingdom
GMAT 1: 730 Q49 V45
GPA: 2.9
WE: Information Technology (Consulting)
A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

25 Feb 2012, 19:00
1
KUDOS
20
This post was
BOOKMARKED
00:00

Difficulty:

85% (hard)

Question Stats:

54% (01:27) correct 46% (01:39) wrong based on 673 sessions

### HideShow timer Statistics

A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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

Struggling on this one too. Any idea how to solve?
[Reveal] Spoiler: OA

_________________

Best Regards,
E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610
GMAT ==> 730

Kudos [?]: 4124 [1], given: 217

Senior Manager
Status: May The Force Be With Me (D-DAY 15 May 2012)
Joined: 06 Jan 2012
Posts: 272

Kudos [?]: 320 [1], given: 16

Location: India
Concentration: General Management, Entrepreneurship
Re: Miles in a gallon [#permalink]

### Show Tags

25 Feb 2012, 21:55
1
KUDOS
Hi !

You need average miles/ gallon with the given data

Total Miles traveled => 10+50 = 60

City Fuel Consumption => 1 gallon - 25 miles => 10 Miles - 10/25 gallons => 0.4 gallons
Highway Fuel Consumption => 1 gallon - 40 miles => 50 Miles - 50/40 gallons => 1.25 gallons

Now the tricky part which even I got wrong in my first timed attempt

Average fuel consumption (City + Highway) = 60 miles / (0.4+1.25) = 60/1.65 = 36.6 miles / gallon

divide 60 / 15 = 40 but since 1.65 is greater than 15 the fraction has to be smaller to its either 38 / 36

38 is just too close so eliminate

Hope this helps
_________________

Giving +1 kudos is a better way of saying 'Thank You'.

Kudos [?]: 320 [1], given: 16

Math Expert
Joined: 02 Sep 2009
Posts: 41892

Kudos [?]: 129172 [11], given: 12194

Re: Miles in a gallon [#permalink]

### Show Tags

25 Feb 2012, 22:57
11
KUDOS
Expert's post
6
This post was
BOOKMARKED
enigma123 wrote:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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

Struggling on this one too. Any idea how to solve?

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 $$\frac{10+50}{0.4+1.25}\approx{36}$$

_________________

Kudos [?]: 129172 [11], given: 12194

Senior Manager
Joined: 07 Sep 2010
Posts: 329

Kudos [?]: 1032 [1], given: 136

Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

07 Apr 2012, 02:39
1
KUDOS
My take on this -

whenever I see this type of question, I make sure what the question is asking me to solve...and this makes the question easier to solve-

Here, its asking - Total distance travelled/ number of gallons used.-----------------(1)

Now start calculating individual entity.

Total distance = 50+10 = 60

Total galoons - This is the tricky part.

Generally, I solve by using unitary method.

such as - 25 miles ---- 1 gallon
1 mile = 1/25
10 miles = 1/25*10

Similarly calculate for Highway.

Try solving for highway and put the values in equation 1. You will get the answer.

Thanks
H
_________________

+1 Kudos me, Help me unlocking GMAT Club Tests

Kudos [?]: 1032 [1], given: 136

Intern
Joined: 08 May 2011
Posts: 6

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

GMAT Date: 04-28-2012
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

26 Apr 2012, 17:51
I got Bunuel's approach.. but was wondering if weighed average should work here that is

(1*25+5*40)/6 = 37.5 ~ 38 Seems it doesnt work here.. But shouldn't it??

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

Math Expert
Joined: 02 Sep 2009
Posts: 41892

Kudos [?]: 129172 [1], given: 12194

Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

26 Apr 2012, 23:09
1
KUDOS
Expert's post
khushboochhabra wrote:
I got Bunuel's approach.. but was wondering if weighed average should work here that is

(1*25+5*40)/6 = 37.5 ~ 38 Seems it doesnt work here.. But shouldn't it??

Actually we are asked to find the average, but the average of miles per gallon (miles/gallon). So, you should have total miles driven in numerator and total gallons used in denominator (miles/gallon). Now, ask yourself: what do you have in numerator and denominator?
_________________

Kudos [?]: 129172 [1], given: 12194

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7676

Kudos [?]: 17381 [6], given: 232

Location: Pune, India
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

27 Apr 2012, 06:34
6
KUDOS
Expert's post
1
This post was
BOOKMARKED
khushboochhabra wrote:
I got Bunuel's approach.. but was wondering if weighed average should work here that is

(1*25+5*40)/6 = 37.5 ~ 38 Seems it doesnt work here.. But shouldn't it??

'Distances traveled' (i.e. ratio of 1:5) cannot be the weights here to find the average mileage. The weights have to be 'number of gallons'.

If we change the question and make it:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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 uses 10 gallons in the city and then 50 gallons on the highway

Now you can use (1*25+5*40)/6

Why?

Whenever you are confused what the weights should be (e.g. here should the weights be the distance traveled or should they be gallons of fuel used...), look at the units.

Average required is $$\frac{miles}{gallon}$$. So you are trying to find the weighted average of two quantities whose units must be $$\frac{miles}{gallon}$$.

$$C_{avg} = \frac{C_1*W_1 + C_2*W_2}{{W_1 + W_2}}$$

$$C_{avg}, C_1, C_2 - \frac{miles}{gallon}$$

So $$W_1$$ and $$W_2$$ should be in gallon to get:

$$\frac{miles}{gallon} = (\frac{miles}{gallon}*gallon + \frac{miles}{gallon}*gallon)/(gallon + gallon)$$

Only if weights are in gallons, do we get 'Total miles' in the numerator and 'Total gallons' in the denominator.

We know that Average miles/gallon = Total miles/Total gallons

[highlight]Takeaway: The weights have to be the denominator units of the average.[/highlight]

So what do we do in this question?

What is the distance travelled (i.e.total miles)?
(10+50) = 60

What is the total gallons used?
Fuel used in the city = 10/25
Fuel used to go from B to C = 50/40

So Average miles/gallon = (60)/(10/25 + 50/40) = apprx 36

You need to know what the weights are going to be. Here, weights have to be the amount of fuel used i.e. in gallons because you are looking for average miles per gallon.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Kudos [?]: 17381 [6], given: 232 Intern Joined: 28 Feb 2012 Posts: 22 Kudos [?]: 12 [0], given: 3 GMAT 1: 700 Q48 V39 WE: Information Technology (Computer Software) Re: A certain car averages 25 miles per gallon of gasoline when [#permalink] ### Show Tags 27 Apr 2012, 09:59 Thanks VeritasPrepKarishma. I was having issues with understanding weights in averages. This cleared it up. Kudos [?]: 12 [0], given: 3 Intern Joined: 06 May 2013 Posts: 24 Kudos [?]: 7 [0], given: 54 Schools: Rotman '16 GMAT 1: 670 Q48 V33 Re: A certain car averages 25 miles per gallon of gasoline when [#permalink] ### Show Tags 28 Aug 2013, 01:36 I just went through this thread and I have a doubt. Applying Karishma's method of using units, in this case, we get (25*10+40*50)/(10+ 50) . The units are (miles/g * miles)/ miles = miles/gallon. Please point out the mistake in my logic. Kudos [?]: 7 [0], given: 54 Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7676 Kudos [?]: 17381 [3], given: 232 Location: Pune, India Re: A certain car averages 25 miles per gallon of gasoline when [#permalink] ### Show Tags 28 Aug 2013, 04:07 3 This post received KUDOS Expert's post pjagadish27 wrote: I just went through this thread and I have a doubt. Applying Karishma's method of using units, in this case, we get (25*10+40*50)/(10+ 50) . The units are (miles/g * miles)/ miles = miles/gallon. Please point out the mistake in my logic. We need total miles in the numerator and gallons in the denominator. (C1*W1 + C2*W2) should make "miles". (W1 + W2) should make "gallons". _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Kudos [?]: 17381 [3], given: 232

Manager
Status: folding sleeves up
Joined: 26 Apr 2013
Posts: 155

Kudos [?]: 137 [0], given: 39

Location: India
Concentration: Finance, Strategy
GMAT 1: 530 Q39 V23
GMAT 2: 560 Q42 V26
GPA: 3.5
WE: Consulting (Computer Hardware)
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

18 Sep 2013, 11:30
enigma123 wrote:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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

Struggling on this one too. Any idea how to solve?

Sol:

10 miles in city while it gives 25miles/gallon in city, so 10 miles will consume : 10/25 =>2/5 gallon

10 miles on highway while it gives 40 miles/gallon on highway, so 10 miles will consume : 10/40 =>1/4 gallon

40 miles on high way whilte it gives 40 miles/gallon on highway, so 40 miles will consume: 40/40 =>1 gallon

Total gallons : 1+ (2/5)+ (1/4) = 33/20

Total distance travelled is (10+50)= 60

so avg is 60/(33/20) ==>36

Kudos [?]: 137 [0], given: 39

Current Student
Joined: 25 Sep 2012
Posts: 287

Kudos [?]: 174 [0], given: 242

Location: India
Concentration: Strategy, Marketing
GMAT 1: 660 Q49 V31
GMAT 2: 680 Q48 V34
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

19 Sep 2013, 03:46
i took 4:37 seconds to solve this question...
Did i spend too much time ?
I actually commited a calculation mistake in between. Even if I wouldn't have done that it would take me at least 3mins.
I see the average of correct and wrond both to be 1:50 (approx)

Kudos [?]: 174 [0], given: 242

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16587

Kudos [?]: 273 [0], given: 0

Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

24 Sep 2014, 04:32
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16587

Kudos [?]: 273 [0], given: 0

Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

25 Dec 2015, 08:05
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

Director
Joined: 07 Dec 2014
Posts: 815

Kudos [?]: 248 [0], given: 12

Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

25 Dec 2015, 11:13
total miles=60
total gallons=10/25+50/40=33/20
total miles/total gallons=36.4 average mpg

Kudos [?]: 248 [0], given: 12

CEO
Joined: 17 Jul 2014
Posts: 2604

Kudos [?]: 396 [0], given: 184

Location: United States (IL)
Concentration: Finance, Economics
GMAT 1: 650 Q49 V30
GPA: 3.92
WE: General Management (Transportation)
A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

18 Nov 2016, 08:11
enigma123 wrote:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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

Struggling on this one too. Any idea how to solve?

well...a pretty straight forward one...instead of RTD chart, we have a RGD one...where G stands for gallons.

1st thing to do, find how much gas the car consumed during the first 10 miles in the city: 10/25 = 2/5
2nd thing to do, find how much gas the car consumed during the 50 miles on the highway: 50/40 = 5/4

total gas consumed: 2/5 + 5/4 = 33/20

now...we have the total distance: 10+50 = 60 miles
we have the total gas consumed: 33/20 gallons
the average consumption is: 60 : 33/20 or 60*20/33 = 20*20/11 = 400/11 -> let's approximate...this takes only few seconds..
400/12 = 100/3 = 33.33
400/10 = 40
so it must be between 33.33 and 40. A, B, and C are out right away.
now...11 * 30 = 330, and we are left with another 70...in 70, 11 fits only 6 times and slightly more.
therefore, the correct answer must be 30+6=36.

D

total time to solve - under 1min50sec.
a relatively easy question, compared to other motion related ones...

Kudos [?]: 396 [0], given: 184

Math Forum Moderator
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 3003

Kudos [?]: 1088 [0], given: 325

Location: India
GPA: 3.5
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

18 Nov 2016, 09:34
enigma123 wrote:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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

Struggling on this one too. Any idea how to solve?

City -

Mileage = 25 m/g
Distance covered is 10 m

So, Fuel required is 10/25 => 0.40

Highway -

Mileage = 40 m/g
Distance covered is 50 m

So, Fuel required is 50/40 =>1.25

Total Miles driven in City + Highway is 60 miles
Total Fuel used in City + Highway is 1.65

Mileage = $$\frac{60}{1.65} = 36.36$$

Hence, answer will be (D) 36

_________________

Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only )

Kudos [?]: 1088 [0], given: 325

Director
Joined: 13 Mar 2017
Posts: 522

Kudos [?]: 121 [0], given: 62

Location: India
Concentration: General Management, Entrepreneurship
GPA: 3.8
WE: Engineering (Energy and Utilities)
Re: A certain car averages 25 miles per gallon of gasoline when [#permalink]

### Show Tags

29 Jul 2017, 04:30
VeritasPrepKarishma wrote:
khushboochhabra wrote:
I got Bunuel's approach.. but was wondering if weighed average should work here that is

(1*25+5*40)/6 = 37.5 ~ 38 Seems it doesnt work here.. But shouldn't it??

'Distances traveled' (i.e. ratio of 1:5) cannot be the weights here to find the average mileage. The weights have to be 'number of gallons'.

If we change the question and make it:
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven 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 uses 10 gallons in the city and then 50 gallons on the highway

Now you can use (1*25+5*40)/6

Why?

Whenever you are confused what the weights should be (e.g. here should the weights be the distance traveled or should they be gallons of fuel used...), look at the units.

Average required is $$\frac{miles}{gallon}$$. So you are trying to find the weighted average of two quantities whose units must be $$\frac{miles}{gallon}$$.

$$C_{avg} = \frac{C_1*W_1 + C_2*W_2}{{W_1 + W_2}}$$

$$C_{avg}, C_1, C_2 - \frac{miles}{gallon}$$

So $$W_1$$ and $$W_2$$ should be in gallon to get:

$$\frac{miles}{gallon} = (\frac{miles}{gallon}*gallon + \frac{miles}{gallon}*gallon)/(gallon + gallon)$$

Only if weights are in gallons, do we get 'Total miles' in the numerator and 'Total gallons' in the denominator.

We know that Average miles/gallon = Total miles/Total gallons

Takeaway: The weights have to be the denominator units of the average.

So what do we do in this question?

What is the distance travelled (i.e.total miles)?
(10+50) = 60

What is the total gallons used?
Fuel used in the city = 10/25
Fuel used to go from B to C = 50/40

So Average miles/gallon = (60)/(10/25 + 50/40) = apprx 36

You need to know what the weights are going to be. Here, weights have to be the amount of fuel used i.e. in gallons because you are looking for average miles per gallon.

VeritasPrepKarishma Your clarification seems impressive as if unit is not same the result will be something different than actual
So first we need to check what is given . If it is miles per gallon then weighted average can only be calculated when amount of fuel used in given.

So, to solve such problem I want to tweak the approach to make the solution aligned with weighted average.

Now since we know that the no. of miles i.e. distance is given and we can't take weighted average method, lets try to make the given rate i.e. miles per galon favorable to distance by reversing it and then using weighted average and then again reversing it to get my answer. All the reversing process will go in mind and we will make full use of Karishma's approach.

So. Car average in city = 25 miles per gallon
Lets reverse it to understand it as car will use 1/25 gallon per mile in city.

Car average on highway = 40 miles per gallon
Lets reverse it to understand it as car will use 1/40 gallon per mile on highway.

Also distance traveled in city is given as 10 miles and on highway is 50 miles.

So, here we can use the weighted average now .
Avg. = (1/25*10 + 1/40* 50 )/(10+50) =( 0.4 +1.25 )/60 = 1.65/60 = 11/400 gallon per mile.

Lets reverse it again to get the answer.
Hence car average = 400/11 = 36.6 miles per gallon.

So, basically I have gone a step further using Karishma's approach to understand the problem, avoid mistake regarding weighted average and then solving it the same way by tweaking it in the mid way.

Hope that helps...
_________________

MBA Social Network : WebMaggu

Appreciate by Clicking +1 Kudos ( Lets be more generous friends.)

Kudos [?]: 121 [0], given: 62

Re: A certain car averages 25 miles per gallon of gasoline when   [#permalink] 29 Jul 2017, 04:30
Display posts from previous: Sort by