NEW HERE? LEARN MORE
closeclose
Last visit was: 25 Apr 2024, 22:59 It is currently 25 Apr 2024, 22:59
Decision Tracker
My Rewards
New posts
New comers' posts

Close
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
Your Progress

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

Two water pumps working together at respective constant

User avatar
shehreenquayyum
Intern
Intern
Joined: 31 May 2006
Posts: 31
Own Kudos [?]: 46 [0]
Given Kudos: 0
Send PM
Two water pumps working together at respective constant [#permalink] New post   23 Jul 2006, 16:57
Two water pumps working together at respective constant rates took 4 hrs to fill a pool. If constant rate of one pump was 1.5 times the constant rate of the other, then how many hours would it have taken the faster pump to fill the pool if it had worked alone at its constant rate?

5
16/3
11/2
6
20/3

I got B, but the answer is E....please explain.



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
User avatar
ghantark
Manager
Manager
Joined: 21 Jul 2006
Posts: 53
Own Kudos [?]: 67 [0]
Given Kudos: 0
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   23 Jul 2006, 17:19
Rate of First Pump = R
Rate of Second Pump = (3/2) R

Work Done = Rate * time

(R + 3/2 R)*4 = 1

R = 1/10

Rate of Fater Pump = (3/2)R = 3/20
Time = W/Rate = 1/(3/20) = 20/3
User avatar
zorro13
Intern
Intern
Joined: 23 Jul 2006
Posts: 40
Own Kudos [?]: 4 [0]
Given Kudos: 0
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   23 Jul 2006, 17:31
HI....

Remember that in this case

1/time machine A + 1/time amchine B = 1/Total time


..
User avatar
Futuristic
Senior Manager
Senior Manager
Joined: 28 Dec 2005
Posts: 418
Own Kudos [?]: 48 [0]
Given Kudos: 0
 Q49  V41
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 01:34
Let rates per hour be a,b.
Then, (a+b)4 = full (f)

now let a=1.5b

2.5b. 10 =f

b=f/10.

(a+f/10)4 =f
4a +2f/5 = f
4a = 3f/5

a=3f/20

comparing a and b, we can see a is the faster rated pump.

in 1hr a completes 3/20 of tank
time taken by to complete tank =1/(3/20) = 20/3
User avatar
rbcola
Manager
Manager
Joined: 01 Jun 2006
Posts: 66
Own Kudos [?]: 3 [0]
Given Kudos: 0
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 09:32
I would have used numbers for this one.

let the smaller pump have a capacity of 200 gallons per hours
Then the faster one is 300 gallons per hour, since it is 1.5 times bigger

Both pump operating for 4 hours will fill up 200*4 + 300*4 = 2000 gallons

You can see the answer the moment you get 2000. The answer is 2000/300 = 20/3
User avatar
balajinaik
Intern
Intern
Joined: 09 Jun 2005
Posts: 9
Own Kudos [?]: 1 [0]
Given Kudos: 0
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 13:25
This is how i calculated. Pls let me know if this is wrong way of doing it.

Formula to find the combined effort of A & B is

AB/A+B
we are given 2 equations.
1. Combined work is 4. so AB/A+B = 4
2. A=1.5B ( Pump A is 1.5 times faster than B)

substituting value of A from equation 2 in equation 1 we get B=20/3
User avatar
ps_dahiya
VP
VP
Joined: 20 Nov 2005
Posts: 1490
Own Kudos [?]: 1133 [0]
Given Kudos: 0
Concentration: Strategy, Entrepreneurship
Schools:Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
 Q50  V34
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 14:26
I did it like this:

Faster pump is 1.5 times faster than the slower.
So slower pump will fill in 4 * 5/2 = 10 hours

So faster pump will fill in 10 * 2/3 = 20/3
User avatar
bondguy
Intern
Intern
Joined: 01 Jul 2006
Posts: 14
Own Kudos [?]: [0]
Given Kudos: 0
Send PM
GMAT ToolKit User
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 20:47
higher rate lesser time
let speed be x , time = y

applying inverse proportion

speed-------------time
| x + 1.5x---------- 4 ^
V 1.5 x--- ---------(y) |

Therefore

x(1 + 1.5)
------------ = y/ 4
1.5x

y = 20/3

if practised upon, it takes hardly 1 min to get the answer
User avatar
jaynayak
Director
Director
Joined: 30 Mar 2006
Posts: 896
Own Kudos [?]: 593 [0]
Given Kudos: 0
Send PM
Re: Two water pumps working together at respective constant [#permalink] New post   24 Jul 2006, 22:50
E.

Let the slower one can complete 1 work in x hrs
Hence the rate is 1/x

Rate of the faster one is 1.5/x

Given they both working together take 4 hrs

Hence
1/x +1.5/x = 1/4
2.5/x = 1/4
x = 10
Hence faster one can finish in x/1.5 = 10/1.5 = 20/3



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
GMAT Club Bot
gmatclubot
Re: Two water pumps working together at respective constant [#permalink]
24 Jul 2006, 22:50
Moderator:
yashikaaggarwal
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions