SOLUTION: a pipe can fill a container with water in 3 hrs. However, if water is drawn from it at the same time at the rate of 4 cubic ft per hour, it requires 5 hrs to fill it. At what rate

Suppose the container holds x cubic feet of water.

So the pipe's fill rate is x cu.ft. per 3 hours. or  or 

That means the new slower fill rate is the pipe's original fill rate 
reduced by  to 

So this new slower fill rate is also x cu.ft. per 5 hours. or  or .

So we equate the two expressions for the new slower fill rate:

 = . 

  

Multiply thru by LCD of 15

5x - 60 = 3x

     2x = 60

      x = 30 cu ft, which is how much the container holds.

Since the pipe's fill rate is , that becomes:

, or 10,

Edwin