GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 25 May 2020, 04:35 ### 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

#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # Pumping alone at their respective constant rates, one inlet pipe fills

Author Message
TAGS:

### Hide Tags

Intern  Joined: 02 Sep 2010
Posts: 34
Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

1
50 00:00

Difficulty:   5% (low)

Question Stats: 87% (01:51) correct 13% (02:31) wrong based on 1449 sessions

### HideShow timer Statistics

Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

A. 3.25
B. 3.6
C. 4.2
D. 4.4
E. 5.5
Board of Directors D
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4989
Location: India
GPA: 3.5
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

9
9
rite2deepti wrote:
one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours

Time required to fill the full tank is 6 hours
rite2deepti wrote:
a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours.

Time required to fill the full tank is 9 hours
rite2deepti wrote:
How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

Use the formula - $$\frac{AB}{(A + B)}$$

Or, $$\frac{6*9}{(6 + 9)}$$

Or, $$\frac{54}{15}$$

Or, $$\frac{18}{5}$$

Or, $$3.6$$

_________________
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 )
##### General Discussion
Intern  Joined: 30 Nov 2010
Posts: 2
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
2
1/2 of capacity in 3 hours

full capacity in 6 hours

---> pump A.

2/3 capacity in 6 hours

(2/3 +1/3) in 6+3 = 9 hours

---> pump B

in 1 hour filled 1/6 +1/9 = 5/18 parts
full in 18/5 hours 3.6 hrs.

HTH
Manager  Status: I rest, I rust.
Joined: 04 Oct 2010
Posts: 91
Schools: ISB - Co 2013
WE 1: IT Professional since 2006
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
1
Inlet 1 fills x/6 in 1 hour
inlet 2 fills (2x/3)/6 = x/9 in 1 hour

so together in 1 hour they will fill x/6 + x/9 = 5x/18
which means to fill 5x/18 it takes 1 hour => to fill x it will take 18/5=3.6 hrs
_________________
Respect,
Vaibhav

PS: Correct me if I am wrong.
Director  G
Joined: 20 Feb 2015
Posts: 722
Concentration: Strategy, General Management
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

3
pipe 1 = 1/6 an hour
pipe 2 = 1/9 an hour

Total time taken =1/6 + 1/9 =3.6 Hours
Intern  Status: GMAT1:520 Q44 V18
Joined: 02 Sep 2015
Posts: 10
Location: United States
Concentration: Strategy, Technology
WE: Information Technology (Computer Software)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

4
Tank A does 1/2 in 3 hrs so we can fine for full capacity it would take 6 hrs.
Similarly , Tank B takes 2/3rd of tank to be filled in 6 hrs so it would fill to full capacity in 6/(2/3) =>18/2 => 9

Now simple work problem states that it would fill the whole tank in :

1/9 + 1/6 = 5/18 unit =>18/5 hrs = 3.6 hrs

Hence Option B
Manager  Joined: 29 Mar 2015
Posts: 74
Concentration: Strategy, Operations
GMAT 1: 700 Q51 V33
WE: Research (Other)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

1
Bunuel wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

(A) 3.25
(B) 3.6
(C) 4.2
(D) 4.4
(E) 5.5

Kudos for a correct solution.

Total capacity = C

Rate of 1 = C/6
Rate of 2 = C/9
Combined rate = 5C/18
Time = 18/5 = 3.6 (B)
CEO  V
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 3977
Location: India
GMAT: QUANT EXPERT
Schools: IIM (A)
GMAT 1: 750 Q51 V41
WE: Education (Education)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

Bunuel wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

(A) 3.25
(B) 3.6
(C) 4.2
(D) 4.4
(E) 5.5

Kudos for a correct solution.

Time taken by First tank Fill 1/2 the tank = 3 hours
i.e. Time taken by First tank to Fill 1 complete the tank = 6 hours

Time taken by Second tank Fill 2/3 the tank = 6 hours
i.e. Time taken by First tank to Fill 1 complete the tank = (3/2)*6 = 9 hours

in 1 Hour, Both tanks together Fill the tank = (1/6)+(1/9) = 5/18 tank
i.e. Time taken by Both tank to Fill 1 complete the tank = 18/5 hours = 3.6 hours

_________________
Prosper!!!
GMATinsight .............(Bhoopendra Singh and Dr.Sushma Jha)
e-mail: info@GMATinsight.com l Call : +91-9999687183 / 9891333772
Online One-on-One Skype based classes l Classroom Coaching l On-demand Quant course
Check website for most affordable Quant on-Demand course 2000+ Qns (with Video explanations)
Our SUCCESS STORIES: Getting Reborn!!! From 620 to 760 l Q-42 to Q-49 in 40 days l 590 to 710 + Wharton l
ACCESS FREE GMAT TESTS HERE:22 FREE (FULL LENGTH) GMAT CATs LINK COLLECTION
Senior Manager  Joined: 20 Aug 2015
Posts: 379
Location: India
GMAT 1: 760 Q50 V44
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
rite2deepti wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

A. 3.25
B. 3.6
C. 4.2
D. 4.4
E. 5.5

Assume the volume of the container to be 6 Lts
We have assumed 6 because 6 is the LCM of 2 and 3, the denominators of the capacity filled.

Inlet 1: 1/2 of capacity in 3 hours i.e. 3 lts in 3 hours
Hence 1 lts/hour

Inlet 2: 2/3 of capacity in 6 hours i.e. 4 lts in 6 hours
Hence 2/3 lts/hour

Inlet 1 + Inlet 2 combined rate = 6/(1 + 2/3) hours= 6/ (5/3) hours = 18/5 = 3.6 hours
Option B
Retired Moderator Joined: 29 Oct 2013
Posts: 245
Concentration: Finance
GPA: 3.7
WE: Corporate Finance (Retail Banking)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

1
let c be tank capacity.
Time taken by First pipe to fill 1/2 the tank = 3 hours. So work done in 1 hr= c*{1/(2*3)}= c/6

Time taken by Second pipe to Fill 2/3 the tank = 6 hours. So work done in 1hr= c*{2/(3*6)}=c/9

in 1 Hour, Both tanks together Fill the tank = (1c/6)+(c1/9) = 5c/18
i.e. Time taken by Both tank to Fill 1 complete the tank = 18/5 hours = 3.6 hours

_________________

My journey V46 and 750 -> http://gmatclub.com/forum/my-journey-to-46-on-verbal-750overall-171722.html#p1367876
Intern  B
Joined: 30 Aug 2015
Posts: 29
Concentration: Marketing, Finance
WE: Brand Management (Manufacturing)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
Time taken by First tank Fill 1/2 the tank = 3 hours
i.e. Time taken by First tank to Fill 1 complete the tank = 6 hours

Time taken by Second tank Fill 2/3 the tank = 6 hours
i.e. Time taken by First tank to Fill 1 complete the tank = (3/2)*6 = 9 hours

in 1 Hour, Both tanks together Fill the tank = (1/6)+(1/9) = 5/18 tank
i.e. Time taken by Both tank to Fill 1 complete the tank = 18/5 hours = 3.6 hours

Director  P
Status: Professional GMAT Tutor
Affiliations: AB, cum laude, Harvard University (Class of '02)
Joined: 10 Jul 2015
Posts: 768
Location: United States (CA)
Age: 40
GMAT 1: 770 Q47 V48
GMAT 2: 730 Q44 V47 GMAT 3: 750 Q50 V42 GRE 1: Q168 V169 WE: Education (Education)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

5
3
Attached is a visual that should help.
Attachments Screen Shot 2016-05-10 at 5.50.37 PM.png [ 100.66 KiB | Viewed 23128 times ]

EMPOWERgmat Instructor V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 16711
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
1
Hi All,

This question can be solved in a couple of different ways, but it's essentially just a Work Formula question.

Work = (A)(B)/(A+B) where A and B are the respective times it takes for two entities to individually complete a task.

To start, we have to figure out how long it takes each pipe to fill the FULL tank....

First pipe = fills 1/2 the tank in 3 hours... so it fills the FULL tank in 6 hours
Second pipe = fills 2/3 the tank in 6 hours... so it fills the FULL tank in 9 hours

Working together, the two pipes will fill the tank in (6)(9)/(6+9) = 54/15 = 3 9/15 hours = 3.6 hours

GMAT assassins aren't born, they're made,
Rich
_________________
Director  G
Joined: 02 Sep 2016
Posts: 625
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

2
Rate= Work/Time

Let total work = x
Inlet pipe 1

Time= 3 hours
Work done= 1/2 *x

Rate= x/2/3= x/6

Inlet pipe 2

Time= 6 hours
Work done= 2/3 of x

Rate= 2x/3/6 = x/9

Combined rate=x/6 + x/9= 5x/18

Again the same formula:

Rate= Work/Time
5x/18= x/Time
Time= x/5x/18= 18/5= 3.6

Another method is to consider the total work as the LCM (2,3) (Denominators)

Total work= 6

Inlet pipe 1
Time= 3
Work done= 1/2 *6= 3

Rate= 3/3= 1

Inlet pipe 2
Time= 6
Work done= 2/3 * 6= 4
Rate= 4/6= 2/3

Combined rate= 1+2/3= 5/3

Work= 6

Time= 6/5/3= 18/5= 3.6
Target Test Prep Representative V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10543
Location: United States (CA)
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

1
1
rite2deepti wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

A. 3.25
B. 3.6
C. 4.2
D. 4.4
E. 5.5

The rate for the first inlet pipe is (1/2)/3 = 1/6 and the rate for the second pipe is (2/3)/6 = 2/18 = 1/9.

If we let t = the number of hours they work together to fill the empty tank, we have:

(1/6)t + (1/9)t = 1

t/6 + t/9 = 1

Multiplying the entire equation by 18, we have:

3t + 2t = 18

5t = 18

t = 18/5 = 3 ⅗ = 3.6

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Director  P
Status: Professional GMAT Tutor
Affiliations: AB, cum laude, Harvard University (Class of '02)
Joined: 10 Jul 2015
Posts: 768
Location: United States (CA)
Age: 40
GMAT 1: 770 Q47 V48
GMAT 2: 730 Q44 V47 GMAT 3: 750 Q50 V42 GRE 1: Q168 V169 WE: Education (Education)
Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

Top Contributor
I have a rather random question for dabral and Bunuel: why can't we use the harmonic mean (average of rates) formula here? Is it sheer coincidence that the answer I am getting (3.75) with this equation is so close to the actual answer (3.6)?

1st pipe rate = 1/6 tank per hour

2nd pipe rate = 1/9 tank per hour

Harmonic mean (average of rates) = #/sum of inverse of rates = 2 / (6 + 9) = (2/15) x 2 = 4/15 per hour. (4/15)x = 1, x = 15/4 = 3.75

Yet the answer is 3.6 with the more traditional (and admittedly easy and straightforward) method. Still, what am I doing wrong? Thanks!
Target Test Prep Representative G
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2800
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

Bunuel wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

(A) 3.25
(B) 3.6
(C) 4.2
(D) 4.4
(E) 5.5

We are given that the first inlet pipe fills an empty tank to 1/2 capacity in 3 hours. Since rate = work/time, the rate of the first inlet pipe is (1/2)/3 = 1/6.

We are also given that the second inlet pipe fills the same empty tank to 2/3 capacity in 6 hours. Thus, the rate of the second inlet pipe is (2/3)/6 = 1/9.

We need to determine how many hours it will take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity.

If we let t = the time in hours the two inlet pipes are working together, then the work of the first inlet pipe = (1/6)t and the work of the second inlet pipe = (1/9)t.

Since the tank is filled, we can set total work to 1 and create the following equation:

(1/6)t + (1/9)t = 1

Multiplying the entire equation by 18, we obtain:

3t + 2t = 18

5t = 18

t = 18/5 = 3.6

_________________

# Jeffrey Miller

Jeff@TargetTestPrep.com

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

GMAT Club Legend  V
Joined: 11 Sep 2015
Posts: 4871
GMAT 1: 770 Q49 V46
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

Top Contributor
rite2deepti wrote:
Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?

A. 3.25
B. 3.6
C. 4.2
D. 4.4
E. 5.5

Let's assign a nice value to the volume of the tank. We want a volume that works well with the given information (1/2, 2/3, 3 hours and 6 hours).
So, let's say the tank has a total volume of 18 gallons

One inlet pipe fills an empty tank to 1/2 of capacity in 3 hours
1/2 the tank is 9 gallons.
So, this pipe fills 9 gallons in 3 hours.
So, the RATE of this pipe = 3 gallons per hour

A second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours
2/3 the tank is 12 gallons.
So, this pipe fills 12 gallons in 6 hours.
So, the RATE of this pipe = 2 gallons per hour

So, the COMBINED rate of BOTH pumps = 3 gallons per hour + 2 gallons per hour = 5 gallons per hour

How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?
We need to pump 18 gallons of water, and the combined rate is 5 gallons per hour
Time = output/rate
= 18/5
= 3.6 hours

Cheers.
Brent
_________________
Intern  S
Joined: 18 Oct 2019
Posts: 27
Location: India
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

1/2 of capacity in 3 hours

full capacity in 6 hours

---> pump A.

2/3 capacity in 6 hours

(2/3 +1/3) in 6+3 = 9 hours

---> pump B

in 1 hour filled 1/6 +1/9 = 5/18 parts
full in 18/5 hours 3.6 hrs.

Posted from my mobile device
Intern  B
Joined: 14 Aug 2017
Posts: 8
Re: Pumping alone at their respective constant rates, one inlet pipe fills  [#permalink]

### Show Tags

Again a longer solution

What we know
> Tank size is the same hence Tank Size is = 1

Part 1.
>Inflow one takes 3 hrs to fill half
> hence it takes the 6 hrs to fill the tank
> hence it fills @ 1/6 per hour

Part 2
> inflow takes 6 hrs to fill 2/3
> hence the remaining 1/3 will take 3 hrs
> hence 6+3= 9 hrs to fill 100%
> hence it fils @ 1/9 per hour

We solve
(1/9)x + (1/6)x = 1
18*(1/9)x + 18(1/6)x = 1*18
2x+3x = 18
5x = 18
x =18/5
x = 3.6 Re: Pumping alone at their respective constant rates, one inlet pipe fills   [#permalink] 15 May 2020, 23:38

# Pumping alone at their respective constant rates, one inlet pipe fills  