Pumping alone at their

Expert replies

boomgoesthegmat: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Mon Apr 25, 2016 2:22 pmFollowed by: 1 member; Thanked: 1 times

by boomgoesthegmat » Wed May 04, 2016 4:38 am

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

OA: B

Like this post

Source: Beat The GMAT — Problem Solving | Wed May 04, 2016 4:38 am

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed May 04, 2016 6:10 am

boomgoesthegmat 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 the tank = 18 liters.
Since the first pipe takes 3 hours to fill 1/2 of the 18-liter tank, the rate for the first pipe = w/r = (1/2 * 18)/3 = 3 liters per hour.
Since the second pipe takes 6 hours to fill 2/3 of the 18-liter tank, the rate for the second pipe = w/r = (2/3 * 18)/6 = 2 liters per hour.
Since the combined rate for the two pipes = 3+2 = 5 liters per hour, the time for the two pipes together to fill the tank = w/r = 18/5 = 3.6 hours.

The correct answer is B.

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

Like this post

Danny@GMATAcademy: Junior | Next Rank: 30 Posts; Posts: 23; Joined: Tue Jun 28, 2016 6:39 amFollowed by: 3 members; Thanked: 8 times; GMAT Score:780

by Danny@GMATAcademy » Sat Jan 07, 2017 1:14 pm

Here are a couple of ways to solve this problem:

Method 1 (add the rates): https://www.youtube.com/watch?v=zqeIIbSdEc4
Method 2 (Time Formula): https://www.youtube.com/watch?v=1LeaTvlAA-U

Last edited by Danny@GMATAcademy on Sat Jan 07, 2017 1:23 pm, edited 1 time in total.

Email: [email protected]

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Sat Jan 07, 2017 1:20 pm

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

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

GMAT/MBA Expert

Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 amFollowed by: 34 members; Location: Grand Central / New York; Thanked: 470 times

by Jay@ManhattanReview » Tue Jan 10, 2017 11:09 pm

boomgoesthegmat 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

OA: B

The rate of inlet pipe 1 = 3/(1/2) = 6 hours. It can alone fill the empty tank in 6 hours.

The rate of inlet pipe 2 = 6/(2/3) = 9 hours. It can alone fill the empty tank in 9 hours.

Once both are in operation, the part of the tank filled by them is given by:

1/6 + 1/9 = 5/18

=> The empty tank would be filled by both in 18/5 = 3.60 hours.

Answer: B

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Singapore | Doha | Lausanne | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

Like this post

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8138; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Mon Jan 16, 2017 4:56 pm

boomgoesthegmat 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 one inlet pipe fills an empty tank to 1/2 capacity in 3 hours. Since rate = work/time, the rate of the one inlet pipe is (1/2)/3 = 1/6.

We are also given that a second inlet pipe fills the same empty tank to 2/3 capacity in 6 hours. Thus, the rate 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

Answer:B

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

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review