Question 682497
I'm sorry but I can't see how it could be 80 minutes, and I don't see anything wrong with your equation.  


Let x = time it takes for the pool to fill given that the drain is open and the hose is turned on.


1/15 = amount of the pool filled in 1 minute with hose only and drain closed.

1/20 =  amount of the pool emptied in 1 minute with the drain open and no hose.


{{{1/15 - 1/20 = 1/x}}}, solve for x.  The LCD is 60x, and the answer is x=60.


Why don't you re-post the problem.  Maybe someone else has another idea on this one.


Dr. Robert J. Rapalje, Retired
Seminole State College of Florida


P.S.  Check out my website for full color explanations and lots of practice tests with detailed solutions for all levels of math at www.mathinlivingcolor.com.