Question 1131119
Pump Filling Rate     {{{1/12}}}

valve FILLING Rate    {{{-1/20}}}

Pump&Valve Together    {{{1/12-1/20=(5/5)(1/12)-(3/3)(1/20)=2/60=1/30}}}


The combined filling rate for pump and valve together is ONE pool in 30  hours.
Notice, the valve filling rate is NEGATIVE.