It is currently 19 Nov 2017, 15:10

### 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

# Pumps A, B, and C operate at their respective constant

Author Message
Director
Joined: 01 May 2007
Posts: 793

Kudos [?]: 386 [1], given: 0

Pumps A, B, and C operate at their respective constant [#permalink]

### Show Tags

21 May 2008, 06:31
1
KUDOS
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours, pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously, to fill the tank?

1/3
1/2
2/3
5/6
1

Kudos [?]: 386 [1], given: 0

Senior Manager
Joined: 07 Jan 2008
Posts: 318

Kudos [?]: 154 [0], given: 0

Location: Ann Arbor, Michigan
Schools: Ross Class of 2011

### Show Tags

21 May 2008, 06:56
E.

Ok this one is hard to explan as I use the PR method for work problems (aka Plumber's butt) basically it is a way to show work rate and time in a visual method.

so here we go. I gave the pool a capacity of 10 gallons (you can use any capacity).

First statement tells us 10/(6/5) = rate A+B or A+B = 50/6
Second tells us 10/(3/2) = rate of A+C 0r A+C = 40/6
final statement tells us 10/2 = rate of B+C (to keep numbers easy) 30/6 or B+C = 30/6

Now you have three equations. A+B = 50/6; A+C = 40/6; B+C = 30/6

combine the first two to get B-C= 10/6 then combine with the next one and you get 2B = 40/6 => B= 20/6

now that you have B plug back into your original equations and you get these rates.

A=30/6
B=20/6
C=10/6

A+B+C = 10 gallons per hour or (60/6) because I used 10 as the capacity of the pool it will take them 1 hr together.

****The explanation is far more complicated than it seems, I really like the PR method for solving work problems it is a good way to keep up with your work*****

Great Question I don't think you will see harder work problems on the real thing. +1

Kudos [?]: 154 [0], given: 0

Director
Joined: 01 May 2007
Posts: 793

Kudos [?]: 386 [0], given: 0

### Show Tags

21 May 2008, 07:00
I think there is a easier way to solve...I was able to get in quicker, but I can't really explain it...Can a expert tackle this one?

Kudos [?]: 386 [0], given: 0

CEO
Joined: 29 Mar 2007
Posts: 2553

Kudos [?]: 528 [0], given: 0

### Show Tags

21 May 2008, 07:01
jimmyjamesdonkey wrote:
Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours, pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously, to fill the tank?

1/3
1/2
2/3
5/6
1

1/A+1/B=6/5

1/A+1/C=3/2

1/B+1/C=2

We want 1/A+1/B+1/C

I cant seem to get this correct though my numbers keep getting really screwed up.

Kudos [?]: 528 [0], given: 0

Senior Manager
Joined: 07 Jan 2008
Posts: 318

Kudos [?]: 154 [0], given: 0

Location: Ann Arbor, Michigan
Schools: Ross Class of 2011

### Show Tags

21 May 2008, 07:07
Well I had to explain it in a detailed way which is a little different than the way I did it -but the PR method works and it's fast. I'd say it only took 1-2 mins.

is the OA =1

Kudos [?]: 154 [0], given: 0

Senior Manager
Joined: 07 Jan 2008
Posts: 318

Kudos [?]: 154 [0], given: 0

Location: Ann Arbor, Michigan
Schools: Ross Class of 2011

### Show Tags

21 May 2008, 07:09
Also if you don't like the plug in method I used you could use x if it makes more sense to you.

A+B=5x/6
A+C=2x/3
B+C=x/2

Kudos [?]: 154 [0], given: 0

Director
Joined: 01 May 2007
Posts: 793

Kudos [?]: 386 [0], given: 0

### Show Tags

21 May 2008, 07:17
I solved like this-->

A+B = 1/(6/5)
A+C = 1/(3/2)
B+C = 1/2

Combine:

2a + 2b + 2c = 2

a + b + c = 1

This seems to work, but is it mathematically correct?

Kudos [?]: 386 [0], given: 0

Senior Manager
Joined: 07 Jan 2008
Posts: 318

Kudos [?]: 154 [0], given: 0

Location: Ann Arbor, Michigan
Schools: Ross Class of 2011

### Show Tags

21 May 2008, 07:22
lsuguy7 wrote:
Also if you don't like the plug in method I used you could use x if it makes more sense to you.

A+B=5x/6
A+C=2x/3
B+C=x/2

Make x=1 and it is exactly the same!

I just added an X to show how the PR Method works but you don't need it, you basically made the container x=1 the A+B = 5/6 is the rate and so on.

So yes it is mathematically correct.

Kudos [?]: 154 [0], given: 0

Director
Joined: 01 May 2007
Posts: 793

Kudos [?]: 386 [0], given: 0

### Show Tags

21 May 2008, 07:27
lsuguy7, do you have this PR method documented someplace?

Kudos [?]: 386 [0], given: 0

Senior Manager
Joined: 07 Jan 2008
Posts: 318

Kudos [?]: 154 [0], given: 0

Location: Ann Arbor, Michigan
Schools: Ross Class of 2011

### Show Tags

21 May 2008, 07:30
I don't currently have anything I'll see if I can do a write up on it soon.

Kudos [?]: 154 [0], given: 0

CEO
Joined: 29 Mar 2007
Posts: 2553

Kudos [?]: 528 [0], given: 0

### Show Tags

21 May 2008, 07:37
jimmyjamesdonkey wrote:
I solved like this-->

A+B = 1/(6/5)
A+C = 1/(3/2)
B+C = 1/2

Combine:

2a + 2b + 2c = 2

a + b + c = 1

This seems to work, but is it mathematically correct?

There we go. jeez. i was mking it so hard on myself. That is probably the quickest way to solve this problem.

Nice job.

Kudos [?]: 528 [0], given: 0

Re: GMATPrep: RTD   [#permalink] 21 May 2008, 07:37
Display posts from previous: Sort by

# Pumps A, B, and C operate at their respective constant

Moderator: chetan2u

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