SOLUTION: a pipe can fill a water tank in 8 hours. Due to a leak in the bottom of the water tank it is filled in 10 hours. If the water tank is full how much time will the leak take to empty

Let P be the rate of the pipe (in the unit "tank volume per hour").
Let L be the rate of the leak (in the same unit).


Then you have two equations:

P - L =     (1)   (The pipe fills the tank in 10 hours, when the leak is in action).

P = .        (2)   ("The pipe can fill a water tank in 8 hours.")


Substitute (2) into equation (1). You will get

 - L =   --->  L =  =  = .


So, due to the leak, amount of water of  of the tank volume goes out.

It means, that the full tank will become empty in 40 hours due to the leak.