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.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

A constructor is using three water filling pumps, X,Y, and Z [#permalink]
23 Jan 2011, 01:54

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

100% (02:09) correct
0% (00:00) wrong based on 1 sessions

A constructor is using three water filling pumps, X,Y, and Z, working together at their respective constant rates to fill an initially empty tank in 9 hours.Pumps X and Y,working together at their respective constant rates can fill the same tank in 10 hours.How many hours will pump Z, working alone at its constant rate, take to fill the same tank?

Re: Three water filling pumps, X,Y, and Z, working together [#permalink]
23 Jan 2011, 03:03

Expert's post

MichelleSavina wrote:

Q) A constructor is using three water filling pumps, X,Y, and Z, working together at their respective constant rates to fill an initially empty tank in 9 hours. Pumps X and Y,working together at their respective constant rates can fill the same tank in 10 hours. How many hours will pump Z, working alone at its constant rate, take to fill the same tank?

A) 90

Please Explain....

Let the times needed for the pumps X, Y, and Z, working ALONE at their respective constant rates to fill the empty tank be x, y and z respectively.

Given: \frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{1}{9} (remember we can add the rates) and \frac{1}{x}+\frac{1}{y}=\frac{1}{10}.

Subtract 2 from 1: \frac{1}{z}=\frac{1}{9}-\frac{1}{10}=\frac{1}{90} --> z=90.

Or: you can notice that as all 3 pumps can fill the empty tank in 9 hours and only X and Y can fill the tank in 10 hours, so they need 1 more hour, then Z is doing in 9 hours the work done by X and Y in this 1 extra hour, so as X and Y need total of 10 hours to fill the empty tank then Z alone will need 9*10=90 hours to fill the empty tank alone.

I couldn’t help myself but stay impressed. young leader who can now basically speak Chinese and handle things alone (I’m Korean Canadian by the way, so...