Question 1070684
Inlet pipe can fill 1 tank in 20 minutes.
Outlet pipe can empty 1 tank in 40 minutes.


What is the actual question?  Can you write the problem description and question properly?


Rate for the inlet pipe is  {{{1/20}}}.
Rate for the outlet pipe is {{{-1/40}}}.
The COMBINED rate of the two pipes together is  {{{1/20-1/40=2/40-1/40=1/40}}}, which means that if both pipes are open, and if volume starts as 1 EMPTY tank, the tank would be filled in 40 minutes.