Filling a Tank

Date: 08/01/97 at 20:14:14
From: EVAN
Subject: Filling a Tank

If one pipe can fill a tank in 1 1/2 hours, and another can fill the 
same tank in 45 minutes, how long will it take the two pipes to fill 
the tank together?

Date: 08/07/97 at 15:37:16
From: Doctor Rob
Subject: Re: Filling a Tank

This is a common type of problem given in algebra classes.  Think 
about the part of the tank the first pipe can fill in one minute.  
That would be 1/90 of the tank.  Now think about the part of the tank 
the second pipe can fill in a minute: 1/45 of the tank.  Working 
together, both pipes can fill 1/90 + 1/45 of the tank in one minute.  

Let T be the number of minutes to fill the whole tank together. Then

   T*(1/90 + 1/45) = 1 tankful.

Now solve for T.

All problems of this type can usually be solved by a similar 
technique.

-Doctor Rob,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/